For years, diatom-based biostratigraphy has been settings bio-events based on a qualitatively approach. This means that the biostratigraphy would set an age based on the findings or not of a certain species. However, how many species are needed to consider a certain datum as certain? One, ten, 100? Moreover, each biostratigrapher sets its on limits. One might consider one as enough and another 10. Therefore, the scale more often used is the absent, rare, frequent, common, dominant or abundant with an explanation of what of these definitions mean. This is very common in, for example, IODP expeditions.

However, what would happen to these biostratigraphy levels if one would apply, for example, a concept of 95% confidence level? Moreover, what would happen to an age model if this concept would be applied to all the biostratigraphy microfossil?

Here we will show Expedition 346 age model differences with and without confidence levels applied to diatoms. The differences can be significant and even considering the existence of a hiatus can be reconsider if confidence limits are applied, turning a possible hiatus into a very slow sedimentation rate having serious implications to the initial paleoceanographic interpretations.

How to cite: Lopes, C. and Velez, J.: On the application of confidence limits to biostratigraphy: an example from diatoms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13000, https://doi.org/10.5194/egusphere-egu2020-13000, 2020.

Micropaleontological and isotopic analyses were performed on 93 samples covering the first 50m of borehole U1460 in aim to reconstruct the paleo-environmental and paleo-climatic conditions of western australian shelf. Borehole U1460 was drilled at a water depth of 214 m during IODP (International Ocean Discovery Program) 356 expedition.

The distribution of benthic foraminifera and ostracod assemblages associated with planktonic foraminifera variation allow to characterized two main climatic phases : one dominated by generally cold conditions (glacial-like, from 50 to 20m) and another interglacial-like phase (from 20 to 0m), characterized by warmer climate. Those have been identified on the basis of distribution of tropical warm water Goloborotalia menardii (planktonic foraminifera) that shows high abundance only from 20 to 0 m, attributed to the interglacial-like phase, coherent with δ¹⁸O values curve.

The glacial assemblage is composed by an assemblage dominated by ostracod genera/species such as Pterigocytherei ssp., Krithe spp.,Argilloecia sp., Pseudocythere caudata, Trachyleberi ssp. and by benthic foraminifera such as Cibicides lobatulus, Elphidiumsp., Hyalineasp., Rosalina bradyi. These assemblages indicate cold bottom conditions with probably poorly oxygenated and organic-rich sediment environment.

The interglacial assemblage is characterized by ostracods species as Neonesidea sp., Bradleya sp., Cytherella sp., and by benthic foraminifera as Meloni ssp., Uvigerina spp., Quinqueloculina sp., Textularia sp., Trifarina sp., Cassidulina sp., Brizalina sp., Bulimina sp., Sigmoilopsis schlumbergeri. This assemblage suggests warm bottom conditions under well-oxygenated, high energy regimes and food input that would be important.

Those two phases include probably multiple glacial and interglacial stages but the most spectacular result indicates that after the onset of MIS12, one of the major glaciation in the Quaternary), the oceanographic conditions in the Western Australia sector changed deeply, either because of oceanic current re-organization or because of the continental climate change (dry/wet climate transition) that controls the amount of micronutrient input into the ocean.

How to cite: Angue Mintoo, C., Courtillat, M., and Bassetti, M.-A.: Paleoceanographic variations in SE sector of Indian Ocean (Australian shelf, IODP-U1460 site): is the MIS12 the trigger for long-term oceanic circulation re-organisation? Insights from benthic meiofauna (ostracods and foraminifera), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22609, https://doi.org/10.5194/egusphere-egu2020-22609, 2020.

Studies on organic preservation in fossil tissues have been a contentious topic, as fossils have been thought to preserve little, if any, organic content after diagenesis. Several studies have previously reported the presence of collagen in fossils from deep time including in Cretaceous dinosaur bones (e.g.: Schweitzer et al., 2007, Science v. 316, 277-280). These findings have also been the subject of criticism with respect to the reproducibility of their results (e.g.: Buckley et al., 2017, Proceedings of the Royal Society B v. 284: 20170544). In the present study, we analysed a turtle shell from Eocene to ascertain a suitable proxy for the preservation of collagen, by using comprehensive pyrolysis gas chromatography – time-of-flight mass spectrometry (Py-GCxGC-TOFMS) and comparing the pyrolytic products obtained to those of modern turtle shell and collagen standard. 

In order to add to the robustness of the study, industry standards of chitin, melanin and collagen were analysed using Py-GCxGC-TOFMS and their chromatograms compared for characteristic pyrolytic products that can be used to differentiate between them. Collagen could be differentiated from the other nitrogen-bearing biopolymers based on the presence of characteristic cyclic dipeptides known as 2,5-diketopiperazines (DKPs) which are formed by the recombination of peptides during pyrolysis. We compared the chromatogram of collagen standard to that of a modern turtle shell and found that the two chromatograms could be correlated based on the presence of diketodipyrrole, 2,5-DKP(Pro-Pro), 2,5-DKP(Pro-Ala), 2,5-DKP(Pro-Gly), 2,5-DKP(Pro-Hyp), 2,5-DKP(Pro-Arg) and 2,5-DKP(Pro-Lue/Ile). We then compared the chromatogram of modern turtle shell to the Eocene shell and confirmed the presence of diketodipyrrole and 2,5-DKP(Pro-Pro) in the fossil shell thus unambiguously indicating that collagen is preserved.

How to cite: Umamaheswaran, R., Dutta, S., Singh, H., Kumar, S., and Sahni, A.: Chemical evidence for the preservation of collagen in Eocene turtle shell using Py-GCxGC-TOFMS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-425, https://doi.org/10.5194/egusphere-egu2020-425, 2020.

A key topic in paleoecology and macroevolution is whether assemblages of species show patterns of persistence over millions of years; a phenomenon that has been variously referred to as ‘Turnover Pulse’ or ‘Coordinated Stasis’. It has generally been presumed that any abrupt environmental changes discernible in the geological record will often lead to community turnover and the establishing of a new community that is discrete from the previous iteration, even if environmental conditions return to those that existed prior to the disruptive event. A related topic is, if patterns of stability can and do prevail despite disruption, what are the processes that allow for this. Potential options include the degree of change in the physical environment, which may not be great enough to exceed the threshold required for community collapse, or due to ‘Ecological Locking’, where directional selection is constrained by ecological processes.

Our touchstone to consider these topics is the detailed fossil record of Carboniferous brachiopod communities from the Mid-continent of North America. These were highly diverse communities that persisted in a very dynamic environmental setting. In particular, these communities were subjected to frequent and geologically rapid phases of marine transgression and regression associated with climate change over approximately a 20-million-year period. These changes likely resulted in repeated community destruction and renewal as suitable habitat was lost and then subsequently re-established.

Using a suite of statistical techniques, we characterized the nature and scope of changes in these fossil communities over time. We found that, at one scale, fossil communities were not stable throughout this interval, both in terms of taxonomic composition and the associated abundance of those taxa. Thus, there is no evidence of obdurate ecological stasis, as new discrete communities, statistically dissimilar from previous and subsequent iterations, form following each environmental disruption. However, at a higher scale, stability is manifest, as diversity patterns are stable across time and despite episodes of environmental change. In particular, we identify a form of qualified ecological stasis for both the different environments present during this interval and for the larger region as a whole. Ultimately, whilst the individual taxa that comprise each community differ, there is a consistent number of species that can exist in any given community, such that communities remain functionally similar. This indicates that whilst the individual taxa that come to form communities arrive via the exigencies of recruitment, the overall diversity of the communities is set by some higher-level ecological rules. Specifically, the rules for taxon packing are seemingly constant in distinct environments, likely due to energetic controls that limit how many taxa can be maintained in an environmental setting and/or perhaps because the amount of space needed for any individual to develop into an adult is invariant across different taxa within the same clade. Further, these ecological rules lead to stability even in the face of constant disequilibrium, which matches patterns identified in the recovery of marine invertebrate communities from disruptive events in modern systems.

How to cite: Strotz, L. and Lieberman, B.: Ecological stability despite environmental disruption – searching for ecological rules governing Carboniferous brachiopod assemblages from the North American Mid-continent, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2909, https://doi.org/10.5194/egusphere-egu2020-2909, 2020.

Targeted analysis of organic matter in soils and sediments is useful for evaluating past environmental conditions, as specific compounds may be directly linked to organisms and hence to the conditions in which they inhabited the environment.  Variations in molecular fossil distributions have become a powerful tool for understanding changes in palaeoclimate conditions.  This work uses molecular fossils to give an insight into the impact of transgressive events on primary producers inhabiting the studied basin, and hence a more detailed record of sea-level change.

The cores studied consisted of unconsolidated immature sediments from the mid-late Pleistocene (< 500,000 years) and the Holocene.  Molecular fossils, such as chlorophyll pigments and lipids, exhibit fluctuations as a response to changes in palaeoenvironmental conditions, providing a useful marker for sea-level changes.  Fluctuations in the pigment and n-alkane distribution reflect changes in primary producer activity, while the GDGT-based index of branched and isoprenoid tetraether lipids (BIT) differentiates between terrigenous and marine organic matter inputs.  Lipids were analysed by GC-FID and HPLC-MS while analysis of chlorophyll pigments was carried out using a new UHPLC-DAD method.

The results from biomarker analyses show excellent time-resolved agreement with previous lithological and ecological studies, but enabled a more sensitive response of different primary producers to changing conditions to be observed.  The molecular fossils were able to detect the onset and cessation of the studied transgressions earlier than it was possible with microfossil evidence.  Linking the pigment and lipid record with more secure dating will enable a more accurate record of Quaternary relative sea-level change.

How to cite: Conti, M., Bates, M., Barlow, N., Preece, R., Penkman, K., and Keely, B.: Molecular fossils inferring Quaternary sea-level changes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7153, https://doi.org/10.5194/egusphere-egu2020-7153, 2020.

It is generally accepted that sea-level change represents the most important boundary condition that controls stratigraphic architecture in the shallow-marine area and further downdip. The shallow-marine stratigraphic body is then a result of the changing ratio between sediment supply and accommodation space with a range of local (autogenic) processes interplaying with the eustatic (allogenic) sea level. Extracting the sea-level signal from this interplay is typically approached through rigorous interpretation of the indicative meaning of relevant sea-level markers and through comparison with the most appropriate glacio-isostatic adjustment (GIA) model. The latter comparison is insightful for the last glacial period, but for the Pleistocene it suffers from the dilemma that the GIA contribution to sea-level change cannot be predicted for a specific location unless the ice history is known but this is what the shallow-marine record is trying to reconstruct.

Here we aim for Pleistocene sea-level reconstructions that are largely independent of GIA predictions. For this we present Pleistocene shallow-marine records from high-, mid- and low-latitudinal settings. The presentation focuses on four aspects: type and quality of the data (e.g. outcrop, borehole, etc), preservation of the record, separation of allogenic versus autogenic signal and completeness of the eustatic cycle.

We show that in siliciclastic systems the preservation depends on sediment supply and on the coastal energy with which ravinement and regression surfaces obliterate the stratigraphic record. Separating autogenic from allogenic signals depends very much on data quality and the ability to reconstruct the antecedent topography. None of our records show a complete eustatic cycle from lowstand to highstand and back to lowstand where the missing part of the cycle seems to be indicative for the type of shallow-marine record and its location on earth.

We discuss reasons and implications of our findings and emphasise the need for far greater consideration of stratigraphic architecture, carbonate facies and facies correlation.

How to cite: Mauz, B., Shen, Z., Barlow, N., Hodgson, D., and Woodroffe, C.: The sea-level signal in Pleistocene shallow-marine records – examples from carbonate and siliciclastic sequences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13660, https://doi.org/10.5194/egusphere-egu2020-13660, 2020.

Detailed geological field mapping is essential for the study of Relative Sea Level (RSL) indicators, that are in turn the only direct proxies to assess paleo sea level changes and long-term land movements. In the last decades, traditional mapping methods started to be complemented by small Remotely Piloted Aircraft Systems (RPAS, a.ka.a. drones) and high-resolution remote sensing datasets.

In this contribution, we show the results of geological mapping in the island of Curaçao (Netherlands Antilles). Here, we mapped a staircase sequence of coral reef terraces. In particular, we used TerraceM-2 Maptools (a Matlab^® interface for mapping marine terraces) to extract wide-scale marine terrace elevations from TanDEM-X Digital Elevation Models (DEMs) (German Aerospace Center, DLR and Airbus). We detail the elevation information available for each single terrace with RPAS data processed with Agisoft Metashape, that allows obtaining as final products DEMs and orthophotos of selected sites at the inner margin of reef terraces. We then use land-based photogrammetry coupled with traditional facies analysis to identify geological discontinuities on the lower terrace.

The facies analysis allowed to precisely map the unconformity between the Hato (MIS 5.5) and Cortalein (MIS 7) Units (as identified by Muhs et al., 2012). The top of the Hato Unit forms the so-called “Curaçao Lower Terrace”. The top of the Hato Unit, extending few kilometres from the coast, has been mapped with both TanDEM-X and RPAS data up to the paleo-cliff of the Middle Terrace (formerly attributed to MIS 11), where a well-defined notch is preserved. We attribute this notch to the maximum sea ingression during MIS 5e. We compare its elevation with the RSL predicted by Glacio-Isostatic Adjustment (GIA) models.    

We discuss the new data and models for Curaçao in terms of long-term tectonic uplift and eustatic sea level.

Reference: Muhs DR, Pandolfi JM, Simmons KR, Schumann RR (2012) Sea-level history of past interglacial periods from uranium-series dating of corals, Curaçao, Leeward Antilles islands. Quat Res 78:157–169. doi: 10.1016/j.yqres.2012.05.008

Acknowledgments: TanDEM-X digital elevation data is used with permission within the Project DEM GEOL1210 (A. Rovere / M.E. Raymo). The fieldwork for this work was funded by the Helmholtz Exzellenznetzwerks “The Polar System and its Effects on the Ocean Floor (POSY)”. The authors acknowledge also the ZMT,  the Center for Tropical Marine Ecology, and the DAAD, the German Academic Exchange Service.

How to cite: Cerrone, C., Petersen, A.-K., Stocchi, P., Rovere, A., and Casella, E.: 3D mapping of Quaternary coral reef terraces on Curacao Island, Southern Carribean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-640, https://doi.org/10.5194/egusphere-egu2020-640, 2020.

As contribution to the ongoing research programmes RISeR (Dr. Barlow, Univ. Leeds, UK), WARMCOASTS (Dr. Rovere, Marum Bremen, GER) and LOSS (Dr. Stouthamer and consortium, Utrecht Univ., NL), and in more general effort to correctly deal with legacy geological data in the current era of Open Science and Geodata Science, we are populating the WARMCOASTS-WALIS database with entries for the Last-Interglacial sea-level indicator data points as available for the Southern North Sea area. This part of the world in in the immediate near field of the Scandinavian-British ice mass centre at interglacial temperate latitudes.

The majority of the sea-level indicator data points are of siliciclastic sedimentary type: transgressive contacts of marine muds over basal peats, insolation basin lakes becoming brackish marine, regressive peats establishing on tidal flat tops and so on. The abundance of peat and tradition of palynological investigation of these beds is important to date stratigraphical levels. The floating varve-count based PAZ-duration chronology for the Eemian vegetation succession in NW Europe (Zagwijn1996:QSR) allows to resolve floating ages to submillenial scale in the transgressive limb (PAZs E1-E4 and subzones), and to millennial scale in the high stand (coincident with PAZ E5) and regressive limb (starting at the PAZ E5/E6 break; Zagwijn1983:GeologieMijnbouw). Chronostratigraphical database entries for each zone and subzone have been filed in the WALIS database, informing on the varve count durations (floating time scale). Absolute age is left more broad, as there is some uncertainty and wiggle room and difference of opinion in the timing of the palynological NW European Eemian relative to that Termination II in the MIS and coral records (SierEtAl2015:QGeochron; LongEtAl2015:QSR).

Sedimentary environment analogies are drawn with the Holocene transgression and high stand to identify and classify localities as being sea-level indicator points (SLIPs), Marine limiting points, or Terrestrial limiting points. Analogies with the Holocene relative sea-level rise reconstruction practice (e.g. Hijma&Cohen2019:QSR) also echo in the protocols followed to characterize and document the vertical position of the indicator. Data entry requires to assess depth of contact (at present, expressed to a specified datum), implied depth position of past mean sea level (factoring in tidal range, palaeowater depth, background vertical movement, (de)compaction), and uncertainties to that depth (added up according to error propagation rules).

We compare our re-assessed and standardized database entries for longer established sites to the originally reported reconstructed sea-level positions (e.g. Zagwijn1983) and to their discussion in later publications (2000s, 2010s). What is one point in Zagwijn1983, often becomes an assemblage of terrestrial limiting, SLIPs and marine limiting entries in WALIS. We find the North Sea data in some earlier ‘table style’ global compilations to have suffered from generalisations. We find the protocolised database approaches as established by PALSEA activities (e.g. ShennanEtAl(Eds)2015: Handbook of Sea-Level Research; KahnEtAl(Eds)2019: QSR special issue) a more suitable environment to store and open up regional data for correct in-take and reuse by second/third parties - whether LOSS, WARMCOAST, RISeR, or you.

How to cite: Cohen, K.: Opening up a Last-Interglacial Sea Level Database for the Southern North Sea area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3135, https://doi.org/10.5194/egusphere-egu2020-3135, 2020.

The loading of the North American continent with ice sheets causes a geomorphologic response. As a result of this process, a NW-SE gradient of relative sea level developed in the Caribbean during periods of glaciation. In order to distinguish geomorphologic and eustatic contributions it is important to resolve timing and amplitude of relative sea level at different positions in the Caribbean.

The cave systems around Tulum, Quintana Roo, Mexico are presently submerged and well-connected to the nearby Atlantic with a low hydraulic head gradient. Speleothems must have formed during periods of lower sea level, thus providing constraints on the maximum elevation of relative sea level for given periods of time. Conversely, periods of growth cessation could have been caused by sea level rise thus indicating minimum relative sea level during highstands.

Here, we present ²³⁰Th/U dated submerged speleothems that grew during MIS5a-d as well as MIS1/2, MIS6 and MIS11/12.

Growth of a single stalagmite (QUE01) at -10.8±0.1m (relative to today's sea level) was interrupted twice. Petrographical studies and trace element analysis indicate that submergence caused millennial-scale growth stops in QUE01 during MIS5. The proposed highstands are between 109.4±0.3ka and 105.0±0.3ka as well as between 104.5±0.4ka and 96.9±0.4ka.

While a previous study [1] constrains the amplitude to <9.9m, this study further improves the timing. This is the first record in this area that yields bracketing ages for those highstands from a speleothem that is very close to the peak height. In order to reconstruct a Caribbean sea level gradient, the combined Yucatán record acts as a counterpiece to a similar study from the northern end of the Caribbean sea level gradient which reports highstands at that time with a higher relative sea level [4].

Speleothem growth during MIS1/2 (19-8ka) relates to conflicting local sea level markers [2,3] and contains century-scale growth stops. Samples dating back to MIS6 and MIS11/12 highlight the potential for sea level reconstruction in this area before MIS5.

[1] Moseley et al. (2013) Journal of Quaternary Science 28 293-300
[2] Moseley et al. (2015) The Holocene 25 1511-1521
[3] Hering et al. (2018) Journal of Quaternary Science 33 444-454
[4] Wainer et al. (2017) Earth and Planetary Science Letters 457 325-334

How to cite: Steidle, S. D., Warken, S., Frank, N., Förstel, J., Schorndorf, N., Schröder-Ritzrau, A., Moseley, G., Stinnesbeck, W., and Olguín, J. A.: Relative sea level highstands of the Yucatán Peninsula, Mexico, constrained by speleothem growth periods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1678, https://doi.org/10.5194/egusphere-egu2020-1678, 2020.

The world-wide study of the geological record of the Last Interglacial is key to reconstruct the climatic and oceanographic conditions during that time interval. Here we present preliminary results of a comprehensive field analysis of one of the most extensive and least studied Quaternary fossiliferous sequences in Cabo Verde attributed to the Last Interglacial. It is located at Nossa Senhora da Luz, which is a protected inlet at the SE coast of Santiago Island. The studied sequence shows a set of transitions between fluvial and marine environments, and emersion and immersion events within a confined, highly protected bay environment. The presence, in the upper part of the sequence, of a thick layer of very fine-branched rhodoliths indicates particular ecological conditions within this bay (e.g., shallow and turbidity free waters, stable environmental conditions and/or fast growth) that are absent today and presumably played an important role for the presence of particular invertebrate species during that time. The presence of tidal specimens of the clam Senilia senilis in life position at an altitude of ~12m above sea-level allowed a re-interpretation of relative sea-level changes, suggesting that the uplift trend of Santiago Island for the Last Interglacial period onwards (3m/100ky) is possibly 70% lower than previously calculated (10m/100ky). Fossils include five phyla, with molluscs being the most diverse and abundant. Despite the abundance of some species (e.g., the bivalves Saccostrea cuccullata, S. senilis, and Aequipecten opercularis, and the gastropods Persististrombus latus and Thais nodosa), the general biodiversity is low. The presence of S. cuccullata and S. senilis, absent from extant Cabo Verdean faunas, indicates a more humid climate, unlike the dry climate found today. Some horizons are intensively bioturbated with the crustacean burrow Thalassinoides suevicus. Our new data agree with the hypothesised palaeoclimatic framework of more wet conditions than today for the Last Interglacial in the archipelago.

Keywords: Eemian, Cabo Verde Archipelago, sheltered bay, Senilia senilis, volcanic oceanic islands, NE Atlantic

Acknowledgments

C.S.M. and A.C.R. acknowledge, respectively, his PhD grant M3.1.a/F/100/2015 from FRCT/Açores 2020 and her Post-Doc grant SFRH/BPD/117810/2016 by FCT. R.R. and S.Á. acknowledges his IF/01641/2015 and IF/ 00465/2015 grants funded by FCT. A.R. and M.R. were supported by the by DFG grant RA1597/3-1. This work was supported by FCT project PTDC/CTA-GEO/28588/2017 and LISBOA-01-0145-FEDER-028588 UNTIeD and DRCT 2019-2022 – ACORES-01-0145_FEDER-000078 – VRPROTO.

How to cite: Melo, C., Madeira, J., Ramalho, R. S., Rebelo, A. C., Rasser, M., González, E., Uchman, A., Madeira, P., Rolán, E., Silva, L., Silva, C. M. D., Ryan, D., Rovere, A., Cachão, M., and Ávila, S. P.: Last Interglacial fossiliferous sequences from Santiago Island (Cabo Verde Archipelago): the palaeoecology of the Nossa Senhora da Luz section, a rare example of a protected bay in volcanic oceanic islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10423, https://doi.org/10.5194/egusphere-egu2020-10423, 2020.

Current models that project sea-level rise beyond 2100 have large uncertainties because recent observation encompass a too limited range of climate variability to provide robust tests against which to simulate future changes. It is crucial to turn to the geological record where there are large-scale changes in climate, but the current interglacial provides limited evidence for how the Earth-system responds to increased temperatures, and therefore it is necessary to study previous climatically-warm periods. Global temperatures during the Last Interglacial were ~1^oC warmer than pre-industrial values and 3-5^oC warmer at polar latitudes, during which time global mean sea level was likely 6-9 m above present. Though the drivers of warming during the Last Interglacial are different to those of today, it is the amplified warming at polar latitudes, the primary locations of the terrestrial ice masses likely to contribute to long term sea-level rise, which makes the Last Interglacial an ideal palaeo-laboratory to understand coastal response to sea-level rise.  However, our understanding of Last Interglacial sea level change is primarily limited to tropical and sub-tropical latitudes and it is important to understand the response of temperate estuarine settings to rising sea level.

The ERC-funded RISeR project (Rates of Interglacial Sea-level Change, and Responses) focuses on specifically targeting palaeo shorelines buried within the southern North Sea, preserved beyond the limit of the Last Glacial Maximum ice sheets. Buried Last Interglacial sequences in this area provide a valuable record of marine transgression and are being unveiled in new geophysical and geotechnical datasets acquired to support the offshore renewable energy development. This offshore sedimentary archives offer significant advantages over the geomorphologically restricted onshore records allowing us to trace the transgression over a much large area, and should capture the earliest flooding of the Last Interglacial North Sea basin, when the far-field data suggests ice sheet melt was at it maximum. By integrating the already available datasets with newly acquired samples as part of the project, we aim to develop new palaeoenvironmental reconstructions of the Last Interglacial sea-level change from northwest Europe, providing the first chronological constraints on timing, and therefore rates. This has the potential to allow us to ‘fingerprint’ the source of melt (Greenland and/or Antarctica) during the interglacial sea-level highstand.

How to cite: Barlow, N., Cartelle, V., Pollard, O., Gregoire, L., Gomez, N., Hodgson, D., Eaton, S., Busschers, F., Cohen, K., Cotterill, C., Mellett, C., and Haigh, I.: The southern North Sea as a natural palaeo-laboratory to reconstruct the coastal response to Last Interglacial sea-level rise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14805, https://doi.org/10.5194/egusphere-egu2020-14805, 2020.

The Danube Deep-Sea Fan, situated in NW Black Sea, is one of the most developed deep-sea sedimentary structures in Europe (Panin & Jipa, 2002). In 2018, in the framework of the uBiogas Project (24PCCDI/2018), several cores were acquired from the aforementioned area. In this study, high resolution microfaunal analyses coupled with sedimentological and geochemical ones, were performed on two gravity cores that revealed changes since the Last Glacial Maximum. The cores have been collected from two secondary canyons, situated in the E of the Danube Canyon, at 655,7 m (MN183_3_GC_1) and 1315 m water depths (MN183_8_GC_1). In both cores, three stratigraphic units as described by Ross & Degens (1974) were identified (oldest first): Unit 3 (Lacustrine lutite), Unit 2 (Sapropel Mud) and Unit 1 (Coccolith Mud).

The sediments of Unit 3 correspond to the Last Glacial Maximum and are marked by the presence of the cold-water ostracod species. The cores contain a reddish-brown clay and silty interval belonging to the post-glacial melt-water pulse of the Heinrich Event 1. In these deposits the ostracod assemblages display a high diversity and abundance. The CaCO₃ amount is very low, i.e. below 15%, except for the upper part where it reaches more than 50%. The samples of Unit 3 contain nannofossil assemblages that are entirely composed of reworked species from Cretaceous, Paleogene, Early and Middle Miocene intervals.

In Unit 2 (the sapropel), very few specimens of ostracods were identified, towards the top. During this depositional interval CaCO₃ values are dropping again below 15%. The high abundance of the calcareous nannoplankton species Braarudosphaera bigelowii in the upper part of Unit 2 suggests the first strong influx of marine waters into the Black Sea basin.

In the youngest Unit 1, a brackish-marine ostracod assemblage, with low diversity and abundance was identified. This interval is characterized by the presence of polyhaline ostracods with Mediterranean origin. The ostracods from this assemblage tolerate salinities comprised between 17-21 ‰ and characterize a sub-littoral environment. The CaCO₃ values are increasing to more than 50%. During the depositional interval of Unit 1 the environmental was definitely a marine one, probably with a constant salinity of surface waters over 17 ppm, allowing the calcareous nannoplankton species Emiliania huxleyi and Braarudosphaera bigelowii to proliferate. The great abundance of the two taxa and especially of Emiliania huxleyi indicates the existence in the basin of a high nutrient input.

The financial support for this paper was provided by the Romanian Ministry of Research and Innovation, through the Programme 1 – Development of the National System of Research – Institutional Performance, Project of Excellence in Research-Innovation, Contract No. 8PFE/2018 and by the Project uBiogas, contract no. 24PCCDI/ 2018.

Panin, N., Jipa, D., 2002. Danube river sediment input and its interaction with the northwestern Black Sea. Estuarine Coastline Shelf Science 54: 551–562.

Ross, D.A., Degens, E.T., 1974. Recent sediments of the Black Sea. In: Degens E.T. and Ross D.A. (Eds.), The Black Sea: Geology, Chemistry, and Biology. American Association of Petroleum Geologists, Tulsa, USA: 183–199.

How to cite: Briceag, A., Ion, G., Melinte-Dobrinescu, M., Vasiliu, D., and Lupascu, N.: Late Pleistocene – Holocene sea level and climate changes in the Black Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4450, https://doi.org/10.5194/egusphere-egu2020-4450, 2020.

Environmental gradients are among the primary drivers of change in ecological communities through time and space. However, what is rare are combined data sets of community composition and the environmental factors that may have caused ecological turnover, largely because many environmental variables are difficult to measure in the stratigraphic record. In this study we integrate quantitative abundance estimates of benthic macroinvertebrates with a multivariate dataset of geochemical proxies to potentially estimate the environmental drivers of faunal change through the 13 m.y. history of the Middle–Late Jurassic Sundance Seaway, western United States.

Faunal counts of macroinvertebrates were obtained from marine rocks of the Gypsum Spring, Sundance and Twin Creek formations at 19 localities in Wyoming, Montana and South Dakota. From the same localities, calcitic shells of selected species (Gryphaea planoconvexa, Gryphaea nebrascensis, Gryphaea sp., Liostrea strigilecula, Deltoideum sp.), were analysed for stable isotope (carbon and oxygen) and elemental (Mg/Ca, Sr/Ca, Na/Ca, Ba/Ca) geochemistry. The studied interval was subdivided into seven third-order depositional sequences representing carbonate ramp, wave-dominated, siliciclastic shelf, siliciclastic tidal coast, and mixed evaporite-siliciclastic desert systems. Of these, five depositional sequences were fossiliferous.

Ordination plots (nMDS) of the two palaeoecological and geochemical datasets are very similar (procrustes correlation: 0.75, p: 0.0001). Vector fitting of geochemical data on the palaeoecological ordination shows that a main faunal turnover event, corresponding to the shift from carbonate to siliciclastic deposition at the Middle–Late Jurassic transition, correlates with an increase in productivity (increase of δ¹³C) and a decrease in temperature (decrease of Mg/Ca ratio) through time. Position of fauna in the seaway (craton vs. foredeep) correlates instead with variations of δ¹⁸O and Ba/Ca ratio, suggesting a strong salinity gradient, with decreasing salinity moving from the craton towards the foredeep. A critical discussion of these results will also include factors that could potentially affect temporal changes of proxy data, such as species-specific vital effects.

How to cite: Danise, S., Holland, S., and Price, G.: Combining palaeontological and geochemical data to reconstruct environmental gradients, a case study from the Jurassic Sundance Seaway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9795, https://doi.org/10.5194/egusphere-egu2020-9795, 2020.

Despite much scientific effort aimed over the past three decades to better constrain the fossil record of chemosynthesis-based communities, our understanding of their early evolution remains fragmentary. Until recently, a dominant perception was that, unlike the Cenozoic, bivalve-dominated chemosynthetic ecosystems, the Paleozoic to mid-Mesozoic methane seeps and hydrothermal vents were dominated by brachiopods. Similarly, the pattern of brachiopod vs. bivalve predominance at seeps and vents over the Phanerozoic was believed to have crudely followed that observed in normal-marine benthic shelly assemblages. Recent discoveries from the Middle Palaeozoic of Morocco have questioned this simple perception, documenting the presence of late Silurian and Middle Devonian seeps dominated by mass accumulations of large, semi-infaunal, modiomorphid bivalves (Hryniewicz et al., 2017; Jakubowicz et al., 2017). While representing a lineage unrelated to modern seep-obligate bivalve taxa, the mid-Palaeozoic seep bivalves developed a set of morphological adaptations strikingly similar to those of their modern ecological counterparts, and formed analogous, densely-packed, nearly monospecific assemblages, both suggesting their chemosymbiotic lifestyle. The new documentation of Palaeozoic establishment of the bivalve-dominated seep communities provides a fresh look at the concept of modern chemosynthetic ecosystems as a 'glimpse of antiquity', showing that although it is largely not true taxonomically, it clearly is in terms of recurring morphological themes. At the same time, this refined Palaeozoic record makes the factors responsible for the apparent scarcity of seep-related bivalves during the upper Devonian to early Mesozoic, a period of the remarkable success of brachiopod-dominated seep assemblages, ever more enigmatic.

How to cite: Jakubowicz, M. and Hryniewicz, K.: Are modern chemosynthesis-based communities a ‘glimpse of antiquity’? The changing fate of bivalves and brachiopods at ancient methane seeps as recorded in the Middle Palaeozoic of Morocco, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22640, https://doi.org/10.5194/egusphere-egu2020-22640, 2020.

The ecological consequences of climate change on marine ecosystems remains poorly understood, particularly for ecological communities that reside in enclosed basins, which limit marine species in their ability to migrate. Here we use assemblages of late Quaternary fossils mollusks preserved in nearshore sediments to explore how nearshore marine benthic communities responded to past climate changes in the northern Adriatic.   We focus on three time periods: (1) the last interglacial (<125ka BP), when regional temperatures were higher than today, representing a possible analogue for the near-future global warming; (2) the last late glacial 14.5-18.0 ka BP; and (3) the mid-Holocene 6.0-1.0 ka BP, when conditions were similar to today but with a minimal human impact. Temporal dynamics of benthic communities was assessed by applying multivariate and resampling approaches to abundance data for core-derived samples of fossil mollusks. Results demonstrate that the penultimate interglacial benthic assemblages shifted to a new community state during the subsequent glacial period. The shift represented a decline in abundance of exclusively Mediterranean nearshore species and a concurrent increase in abundance of nearshore species of cosmopolitan and boreal affinity. This shift was, most likely, driven by global climate cooling. Following this major community restructuring, the local nearshore communities had reversed back to their previous state during the mid-Holocene, when interglacial climate conditions were fully reestablished again. We conclude that the nearshore community responded to long-term climate changes by displaying a resilient (rather than persistent or stochastic) behavior, with Holocene biota reversing back to the pre-existing interglacial state. However, regional pollution, trawling and the threat of spreading invasive species are already taking their toll and the present-day communities are shifting to a novel, historical unprecedented community state. Nonetheless, our findings indicate that if local and regional threats can be mitigated, the coastal marine communities of the northern Adriatic would be resilient against limited climate warming in the near future.

How to cite: Scarponi, D., Azzarone, M., Nawrot, R., and Kowalewski, M.: Macrobenthic community response to long-term climate change in the Adriatic Sea (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20678, https://doi.org/10.5194/egusphere-egu2020-20678, 2020.

Absolute abundance of fossils observed in cores and outcrops can be governed by extrinsic processes (e.g., net accumulation rates, intensity of taphonomic processes, post-mortem transport), intrinsic determinants of shell production rates (e.g., fecundity, spawning frequency, growth patterns), or some combination of those interdependent factors. Understanding the role of drivers of fossil abundance can enhance stratigraphic and biological interpretations of the fossil record. To assess the importance of extrinsic and intrinsic processes for fossil mollusks, we used a total of over 400 samples (each representing a 10-cm core interval and ∼0.375 dm³ of sediment) derived from 12 cores from the late Quaternary sedimentary succession of the Po basin (Italy). The results indicate that although extrinsic factors such as compaction, net accumulation rates, and sequence stratigraphic context are to some degree controlling mollusk abundance in the cores, they cannot account for extremely shell-rich deposits. The results suggest instead that shell-rich core intervals record, primarily, episodes of high shell production rates. First, samples with very high shell density (> 4000 specimens per dm3) were characterized by extremely low evenness reflecting dominance by one super-abundant species, typically a small r-selective species capable of an explosive population growth (Lentidium mediterraneum and Ecrobia ventrosa). Second, a taphonomic test supported further the biological (R-hardparts model) rather than sedimentological (R-sediment model) origin of very dense shell concentrations: the quality of shell preservation correlates positively with shell density as predicted by R-hardparts model. The results suggest that intervals of high abundance of mollusk shells in cores record intervals of high biological productivity driven by opportunistic shelly species from lower trophic levels. Integrative studies of facies architecture, sequence stratigraphy, and paleontological data can help to differentiate biologically and physically produced fossil concentrations thus allowing for more informed ecological interpretations of the fossil record.

How to cite: Kowalewski, M., Nawrot, R., Scarponi, D., and Azzarone, M.: Determinants of Mollusk Abundance in Quaternary cores of Po Basin, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21707, https://doi.org/10.5194/egusphere-egu2020-21707, 2020.

How to cite: Steenbergen, I., Špánek, R., Sirova, D., Borovec, J., and Petrash, D.: Microbial regeneration and respiration of Fe(III) outcompetes sulphate respiration in ferruginous, high-sulphate oligotrophic ecosystems , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9349, https://doi.org/10.5194/egusphere-egu2020-9349, 2020.

The landscape and climate research in Altai highlands were carried out in 2018 – 2019. The results of our investigation at the Khindiktig-Khol’ Lake Basin (Mongun-Taiga massif, Tuvan Republic) and Bertek depression (plateau Ukok, Altai Republic) are presented. In frame of study 75 samples (56 – subfossil, 13 flower buds, 6 recent) were collected for pollen analysis. Two key questions are to define the possible steppe-tundra palynological pattern based on project BIOME 6000 relying on steppe and tundra data and to compare palynological pattern with the subfossil data from Altai expeditions (2018-2019). The study was financially supported by Russian Foundation for Basic Research (RFBR) (Grant 18-05-00860).

Within international investigation project BIOME 6000 the palynological patterns of tundra and steppe vegetation were composed (Bigelow et al., 2003). Tundra is characterized by several biomes, such as low- and high-shrub tundra (SHRU; Alnus fruticosa, Betula nana, Salix vestita, Eriophorum, Sphagnum), erect dwarf-shrub tundra (DWAR; Betula nana, Salix herbacea, Cassiope, Empetrum, Vaccinium, Poaceae, Cyperaceae), prostrate dwarf-shrub tundra (PROS; Salix herbacea, Dryas, Pedicularis, Asteraceae, Caryophyllaceae, Poaceae, true mosses), cushion-forb tundra (CUSH; Draba, Papaver, Caryophyllaceae, Saxifragaceae, lichens, true mosses) and graminoid and forb tundra (DRYT; Artemisia, Kobresia, Asteraceae, Brassicaceae, Caryophyllaceae, Poaceae, true mosses). Steppe is described by two biomes: temperate grassland (STEP; Asteraceae, Chenopodiaceae, Liliaceae, grasses) and temperate xerophytic shrubland (STEP; Artemisia, Chrysothamnus, Hippophae, Purshia, grasses). In spite of the absence of steppe-tundra palynological pattern, it may include the pollen data both from steppe (Artemisia, Chrisotamnus, Hippophae, Kobresia, Purshia, Brassicaceae, Chenopodiaceae) and tundra (Alnus fruticosa, Betula nana, Salix herbacea, Cassiope, Draba, Dryas, Empetrum, Eriophorum, Papaver, Pedicularis, Vaccinium, Cyperaceae, Saxifragaceae, Sphagnum, lichens) patterns.

In pollen spectra of western Mongun-Taiga trees mean values vary from 36.4% to 45.4%. The predominance of dwarf birch (Betula nana) dust with the average number 28.7% is identified. As for the Bertek depression, the values change from 36.4% in Muzdy-Bulak to 59.3% in Argamdzhi (2019). Data from subfossil samples in 2018 show the dominance of Betula nana pollen (23.0%), whereas in 2019 it is indicated the significant and constant wind drift of Betula sect. Albae particles (average number – 36.7%) through the massif valleys to the region of sample collection.

In pollen spectra of herbs in Mongun-Taiga region mean value equals 57.9%, whereas at the Bertek depression the values differ from 62.8% (2018) to 37.3% (2019). Those spectra mostly consist of dust samples, such as Carex, Cyperaceae and Poaceae. Asteraceae, Caryophyllaceae, Chenopodiaceae and Fabaceae are also present in both regions.

Artemisia and Chenopodiaceae are the prime indicators of steppe conditions. The vegetation description of the landscapes, where the subfossil samples were collected, proves those conditions. Both vegetation and pollen data are also correlated with the DRYT and STEP biomes from project BIOME 6000. The only difference is that Artemisia prevails at the steppe sites of central and eastern part of Bertek depression, whereas Chenopodiaceae is mostly found within the coexistence of tundra and steppe cenoses in Khindiktig-Khol’ area and western part of Bertek depression.

How to cite: Strelkov, I., Nosevich, E., Amosov, M., and Chistyakov, K.: Current palynological pattern of steppe-tundra at the Altai highland depressions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7245, https://doi.org/10.5194/egusphere-egu2020-7245, 2020.

The Pliensbachian–Toarcian transition has been considered a major bottleneck in the early evolution of belemnites, probably related to major palaeoenvironmental and climatic changes during the Early Toarcian. Previous research has focused on the study of belemnites from higher, temperate latitudes, while high-resolution studies on diversity and size of subtropical belemnite assemblages in the northwest Tethys are comparatively rare. The lack of high-resolution (ammonoid subzone) abundance data on diversity and size distributions of belemnite assemblages does not allow separating changes during the Pliensbachian–Toarcian boundary event from those during the Toarcian anoxic event. Sample standardized diversity analyses on new data from Iberian sections suggest the Pliensbachian–Toarcian corresponds to a slight decrease in diversity and an adult size decrease within dominant species. Cluster and non-metric multidimensional scaling analyses, however, indicate that the largest changes in diversity and palaeogeographic distribution of belemnite assemblages occurred during the Toarcian oceanic anoxic event (TOAE) rather than the Pliensbachian–Toarcian boundary. In southern basins like the Lusitanian Basin and Riff Mountains, belemnites even disappear entirely during the TOAE. More generally, the TOAE corresponds with an increase in body size of belemnite assemblages driven by species turnover. The lack of widespread anoxia in southern basins of the northwest Tethys indicates that direct impact of warming or increased pCO2 triggered by volcanism as well as indirect effects on nutrient availability and productivity might have played an important role during both crises.

How to cite: De Baets, K., Rita, P., Duarte, L. V., Neige, P., Piñuela, L., García-Ramos, J. C., and Weis, R.: The impact of the Pliensbachian-Toarcian crisis on belemnite diversity and size distribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7873, https://doi.org/10.5194/egusphere-egu2020-7873, 2020.

The impact of mass extinctions on the body sizes of animals has received considerable attention and debate, as to whether the reduced size of post-extinction organisms is due to the selective extinction of large species, absence of large species as a stochastic effect of low-diversity faunas, or a size decrease within surviving genera and species. Here, we investigated the body sizes of bivalves following the end-Permian mass extinction event and show that the shell size increase of bivalve genera was driven by both evolutionary and ecophenotypic responses. First, some genera show significant increases in body size with the evolution of new species. Further, the same genera record significant within-species increases in average and maximum body size into the late Induan, indicating that ecophenotypic changes were also involved on long-term body size trends. These increases are associated with invigorated ocean circulation, improved oxygenation of the seafloor, and probably increased food supply.

How to cite: Tietje, M., Foster, W. J., Gliwa, J., Lembke, C., Pugh, A., Hofmann, R., Varela, S., Foster, L. C., Korn, D., and Aberhan, M.: Primary productivity, deoxygenation, and the Gulliver-absence effect determine bivalve body size following the end-Permian mass extinction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10213, https://doi.org/10.5194/egusphere-egu2020-10213, 2020.

A small but rather unique reef type occurs in the Silurian of Gotland mainly composed of encrusting bryozoans and microbial crusts, forming a complex intergrowth, which can be characterized as bryozoan-rich stromatolites, so-called “bryoliths”. The alternation of bryozoans and microbes is assumingly driven by a repeated change of hostile and more favorable conditions for metazoan growth. The surfaces of the reef bodies are composed of characteristic cauliflower structures, created by bryozoans, which are performing a finger-like growth in every direction. Other common features are bioerosion (mostly by bivalves), enigmatic encrusting echinoderms, a high abundance of organophosphatic fossil remains such as bryozoan pearls and discinid brachiopods, a high abundance of epi- and endobionts, vadose silt, and gypsum pseudomorphs.

Altogether, ten of these special reefs have been identified on Gotland so far. All of them were formed during periods of strong positive δ ¹³C excursions at the Ireviken and Lau isotope excursions in the early Wenlock and late Ludlow, respectively. The unusual features of the bryoliths as well as their occurrence exclusively during strong positive δ ¹³C excursions indicate very specific environmental requirements. This leads to the assumption, that whatever caused the isotope excursions also has affected these reef systems. Hence, investigating the bryoliths will hopefully increase our knowledge to what has happened during the – still enigmatic – Silurian stable isotope excursions.

How to cite: Claussen, A. L., Munnecke, A., and Ernst, A.: Bryozoan-rich stromatolites (“bryoliths”) from the Silurian of Gotland and their relation to climate-related perturbations of the carbon cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22300, https://doi.org/10.5194/egusphere-egu2020-22300, 2020.

As the world’s largest ocean, the Pacific Ocean is intricately linked to major changes in the global climate system. International Ocean Discovery Program (IODP) Expedition 378 is designed to recover Paleogene sedimentary sections in the South Pacific to reconstruct key changes in oceanic and atmospheric circulation. These cores will provide an unparalleled opportunity to add crucial new data and geographic coverage to existing reconstructions of Paleogene climate and as part of a major regional slate of expeditions in the Southern Ocean to fill a critical need for high-latitude climate reconstructions. Appropriate high-latitude records are unobtainable in the Northern Hemisphere of the Pacific Ocean.

The drilling strategy included a transect of sites strategically positioned in the South Pacific to recover Paleogene carbonates buried under red clay sequences at present latitudes of 40°–52°S in 4650 – 5075 meters of water depth. Due to technical issues we no longer will be able to reach the deeper sites. Therefore, the focus of Expedition 378 will be now to obtain a continuous sedimentary record of a previously single hole, rotary-drilled, spot-cored, classic Cenozoic high-latitude DSDP Site 277 and provide a crucial, multiple hole, mostly APC-cored, continuous record of the intermediate-depth Subantarctic South Pacific Ocean from the Latest Cretaceous to late Oligocene.

How to cite: Röhl, U., Thomas, D. J., and Childress, L. and the Expedition 378 Science Party: IODP Expedition 378 South Pacific Paleogene Climate: New high-resolution high-latitude Cenozoic Section, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8872, https://doi.org/10.5194/egusphere-egu2020-8872, 2020.

Although the Arctic Ocean is a major player in the global climate/earth system, this region is one of the last major physiographic provinces on Earth where the short- and long-term geological history is still poorly known. This lack in knowledge is mainly due to the major technological/logistical problems in operating within the permanently ice-covered Arctic region which makes it difficult to retrieve long and undisturbed sediment cores. Continuous central Arctic Ocean sedimentary records, allowing a development of chronologic sequences of climate and environmental change through Cenozoic times and a comparison with global climate records, however, were missing prior to the IODP Expedition 302 (Arctic Ocean Coring Expedition – ACEX), the first scientific drilling in the central Arctic Ocean in 2004. By studying the unique ACEX sequence, a large number of scientific discoveries that describe previously unknown Arctic paleo-environments, were obtained during the last 15 years (for most recent review and references see Stein, 2019a). While these results from ACEX were unprecedented, key questions related to the climate history of the Arctic Ocean remain unanswered, in part because of poor core recovery, and in part because of the possible presence of a major mid-Cenozoic hiatus or interval of starved sedimentation within the ACEX record. Following-up ACEX and its cutting-edge science, a second scientific drilling on Lomonosov Ridge with a focus on the reconstruction of the continuous and complete Cenozoic Arctic Ocean climate history, has been proposed and now scheduled as IODP Expedition 377 "Arctic Ocean Paleoceanography - ArcOP") for late summer/early autumn 2021. Based on new seismic and coring data obtained during Polarstern Expedition PS87 in 2014 (Stein, 2015) and Polarstern Expedition PS115/2 in 2018 (Stein, 2019b), several locations for potential drill sites have been proposed and further optimized. At the primary drill site location, about 230 m of Plio-Pleistocene, 460 m of Miocene, and >200 m of Oligocene-Eocene may be recovered. These new detailed climate records spanning time intervals from the Paleogene Greenhouse world to the Neogene-Quaternary Icehouse world will give new insights into our understanding of the Arctic Ocean within the global climate system and provide an opportunity to test the performance of climate models used to predict future climate change. Within this presentation an update of the primary objectives and the drilling strategy of ArcOP Expedition 377 will be outlined. For further details as well as the drilling proposal we refer to http://www.ecord.org/expedition377/ .

Reference:

Stein, R. (Ed.), 2015. Cruise Report of Expedition PS115/2 of the Research Vessel POLARSTERN to the Arctic Ocean in 2014 (http://epic.awi.de/37728/1/BzPM_0688_2015.pdf).

Stein, R. (Ed.), 2019b. Cruise Report of Expedition PS115/2 of the Research Vessel POLARSTERN to the Arctic Ocean in 2018. (https://epic.awi.de/id/eprint/49226/1/BzPM_0728_2019.pdf ).

Stein, R., 2019a. The late Mesozoic-Cenozoic Arctic Ocean climate and sea ice history: A challenge for past and future scientific ocean drilling. Paleoceanography & Paleoclimatology, ,  https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018PA003433

How to cite: Stein, R., Weigelt, E., Niessen, F., and St. John, K.: Towards a Continuous Cenozoic Arctic Climate Record - A Challenge for IODP Expedition 377 in 2021, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4886, https://doi.org/10.5194/egusphere-egu2020-4886, 2020.

The Antarctic Circumpolar Current (ACC) is the world’s strongest zonal current system that connects all three major basins of the global ocean, and therefore integrates, forces and responds to global climate variability. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, the Pacific sector of the ACC lacks information on its Cenozoic paleoceanography from deep-sea drilling records.

To advance our knowledge and understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO₂, IODP Expedition 383 recovered sedimentary sequences at: (1) Three sites located in the central South Pacific (Sites U1539, U1540 and U1541); (2) two sites at the Chilean Margin (U1542, U1544); and (3) one site from the hemipelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Age control based on magneto and bio-stratigraphically constrained orbital tuning of physical properties in the Plio-Pleistocene sediments is remarkable, with Sites U1541 and U1543 extending the record back to the late Miocene, and Site U1540 to the earliest Pliocene. Pleistocene sedimentary sequences with high sedimentation rates in the order of 40 cm/kyr were drilled in the Central South Pacific (U1539) and along the Chilean Margin. Taken together, the sites represent a depth transect from ~1100 m at the Chilean margin (U1542) to ~4070 m in the Central South Pacific (U1539), and allow reconstructing changes in the vertical structure of the ACC – a key issue for understanding the role of the Southern Ocean in the global carbon cycle- to be investigated. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic, carbonate, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep ocean variations and their relation to atmosphere and cryosphere changes through stadial-to-interstadial, glacial-to-interglacial and warmer than present time intervals.

How to cite: Lamy, F., Winckler, G., Zarikian, C., and 383 Scientists, E.: Investigating the Dynamics of the Pacific Antarctic Circumpolar Current – Initial Results from International Ocean Discovery Program Expedition 383 (DYNAPACC), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22367, https://doi.org/10.5194/egusphere-egu2020-22367, 2020.

In Early Cretaceous, Shahezi Formation developed in syn-rift stage which belongs to the deep strata of the Songliao Basin, China. Due to the poor outcrop development, there is no previous study or report on the provenance of detrital zircons from Shahezi Formation before. The Songke 2 well is a part of Songliao Basin drilling project which belongs to the International Continental Scientific Drilling Projects (ICDP). The conduct of this scientific drilling is to obtain a nearly complete Cretaceous terrestrial sedimentary record, as determined from basin-filling history. Therefore, this research will focus on the sample from Songke 2 well. This study based on continuous and complete sampling which are unique research materials. What’s more, Songliao Basin is one of the largest continental sedimentary basins in the world, which holds the most important reserves of Chinese oil and natural gas. Consequently, this study is a kind of significance for oil and natural gas prospects of deep strata in Songliao Basin.

Through the detailed description about cores, fan delta facies and lacustrine facies can be identified in this study. Also, the detailed information and sedimentary environment at Early Cretaceous can be clarified. The upper member of Shahezi formation shows the characteristics of fan delta facies intersecting shore-shallow lakes, reflecting the multistage cyclicity changes under the sufficient source supply during the syn-rift stage. In order to define the provenance of the upper member of Shahezi Formation in the north-central area of the Songliao Basin, five sandstone sample (DZ01~05) of the upper member of Shahezi Formation were continuous sampling from Songke 2 well. U-Pb dating was performed on detrital zircons separated from the five sandstone samples. Detrital zircons from DZ01 to DZ05 has dominant ages of 105~140 Ma (268 grains), 155~200 Ma (160 grains), and 220~260 Ma (44 grains). This paper demonstrates that the provenance of the upper member of Shahezi Formation is came from the Central Great Xing’an Range. The depositional period of the Shahezi Formation constraints of maximum sedimentary age and reached to 111-115 Ma. At the same time, the Great Xing’an Range also provides sediments for the western Hailar Basin, which indicates that the Great Xing’an Range uplift and denudation during this period. The closure and collision of the Mongolia-Okhotsk ocean to the north and Pacific Plate subduction beneath the Asian continent to the east were the major tectonic events affecting the tectonic environment of the Great Xing’an Range.

How to cite: An, D.: Early Cretaceous (Aptian) provenance and tectonic response in Songliao Basin, NE China: Evidence from detrital zircon U-Pb ages from the Shahezi Formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5621, https://doi.org/10.5194/egusphere-egu2020-5621, 2020.

Research on offshore tsunami deposits is scarce and their depositional processes and preservation potential are virtually unexplored. Therefore, the RV Meteor cruise M152 mapped and sampled one coast-parallel and two coast-perpendicular transects at water depths from 65 to 114 m off the Algarve coast (Portugal). This coast was strongly affected by the well-known Lisbon earthquake and tsunami of November 1^st, 1755 AD. Numerous onshore locations have been well documented and studied with historic damage reports and modern scientific investigations of the onshore tsunami deposits. However, very scarce information about the backwash, the water masses flowing back into the sea, exists and their imprint on the shelf is unexplored.

In order to fill this gap, a total of 19 vibracores were recovered during the RV Meteor cruise M152. For tracing the sedimentary imprint of the AD 1755 tsunami and potential predecessors, a multi-proxy analysis was carried out (sedimentology, micropaleontology, inorganic and organic geochemistry, radiocarbon and OSL dating). Within the offshore Holocene stratigraphic record, at least two event layers of likely tsunami backwash origin were identified based on their significantly different properties compared to the background shelf sediments. The uppermost tsunami layer (at a depth of 16-25 cm in most cores) displays an erosional contact at the base with heterogeneous compositional changes; its bounding radiocarbon ages allow a correlation with the AD 1755 Lisbon tsunami. Organic-geochemical markers, such as n-alkanes, polycyclic aromatic hydrocarbons, steroids and fatty acids, show an increased input of terrestrial matter in this offshore AD 1755 event layer.

A surprising discovery was another distinct high-energy deposit, i.e. a potential predecessor to the AD 1755 Lisbon tsunami, at a core depth of about 122-155 cm, which was ¹⁴C-dated to approx. 3700 yrs cal BP. Due to its erosional base and coarse-grained composition (well-sorted medium sand), as well as the increased terrestrial influence (displayed by biomarkers), it can be assumed that this deposit originates from the backwash of a paleo-tsunami.

This multi-proxy approach with sedimentological, micropaleontological, inorganic and organic-geochemical criteria, enabled us to (1) identify of backwash tsunami deposits; (2) establish a recurrence interval; and (3) estimate the hazard potential for the related coastal areas. Results of the M152 cruise demonstrate for the first time that the depositional basins on the Algarve shelf have the potential to reliably archive Holocene tsunami backwash deposits. The low-energy environment of the outer Algarve shelf sets prime conditions for the preservation of tsunami backwash deposits. Thus, these geoarchives offer the possibility to study the mechanisms and hydrodynamics of backwash currents, and to investigate tsunami strata that are not preserved elsewhere.

How to cite: Bellanova, P., Reicherter, K., Costa, P. J. M., Frenken, M., Feist, L., Schwarzbauer, J., Santisteban, J. I., Vött, A., Bosnic, I., Brückner, H., Schüttrumpf, H., Andrade, C., Duarte, J. F., Kuhlmann, J., and M152 scientfic Team, T.: Uncharted archives – imprints of tsunami backwash deposits on the Algarve shelf (Portugal), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7686, https://doi.org/10.5194/egusphere-egu2020-7686, 2020.

A drilling hazard assessment has been completed for a large area of the NW Greenland-Baffin Bay continental shelf. This assessment was in relation to International Ocean Discovery Program (IODP) proposal 909 that aims to drill several sites across the shelf in an attempt to better understand the evolution and variability of the northern Greenland Ice Sheet. The assessment utilised high quality and extensive 3D seismic data that were acquired during recent hydrocarbon exploration interest in the area – a fact that highlights the risk of drilling in a petroleum province and therefore, the importance of this assessment with regards to safety.

Scattered seismic anomalies are observed within the Cenozoic sedimentary succession covering the rift basins of the Melville Bay region. These features, potentially representing the presence of free gas or gas-rich fluids, vary in nature from isolated anomalies, fault flags, stacked fluid flow features and canyons; all of which pose a significant drilling risk and were actively avoided during site selection. In areas above the Melville Bay Ridge – a feature that dominates the structure of this area – free gas is also observed trapped beneath extensive gas hydrate deposits, identified via a spectacularly imaged bottom simulating reflector marking the base of the gas hydrate stability zone. The location of the hydrate deposits, and the free gas beneath, are likely controlled by a complicated migration history, due to large scale rift-related faulting and migration along sandy aquifer horizons. In other areas, gas is interpreted to have reached the shallow subsurface due to secondary leakage from a deeper gas reservoir on the ridge crest.

It is clear that hydrocarbon related hazards within this area are varied and abundant, making it a more challenging location to select sites for an IODP drilling campaign. However, due to the extensive coverage and high resolution (up to 11 m vertical resolution (45 Hz at 2.0 km/s velocity) of the 3D seismic data available, as well as the use of recently acquired ultra-high resolution site survey lines, these features can be accurately imaged and confidently mapped. This allowed for the development of a detailed understanding of the character and distribution of fluids within the shallow subsurface, and the use of this knowledge to select site localities that maximise the potential for drilling to be completed safely and successfully if proposal 909 were to be executed.

How to cite: Cox, D., Newton, A. M. W., Knutz, P. C., and Huuse, M.: Planning a drilling campaign in a petroleum province using high resolution 3D seismic data – IODP proposal 909, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20571, https://doi.org/10.5194/egusphere-egu2020-20571, 2020.

Key archives in environmental and past climate research are buried in soft sediment but investigations are often hampered by the lack of continuous, complete and undisturbed samples. We have developed the new core-drilling instrument Hipercorig to overcome these issues and we have tested this tool successfully on the perialpine Lakes Mondsee and Constance at up to 204 m water depths and down to 64 m core length.

Hipercorig comprises a hydraulically hammered down-the-hole piston coring system capable to reach up to 100 m core length in up to 200 m water depths. The well-proven piston system ensures high-quality intact cores while the hydraulic hammer drive allows penetrating hard-layers such as sand, gravel or tephra. The piston-hammer system, casing string and ground plate is connected via Kevlar ropes to a coring rig and deployment is controlled via underwater cameras. For lake, estuarine and shallow marine projects buoyance and working space is provided through a barge with four anchors and winches. The complete system is consisting of modular elements to be shipped in four 20-foot-containers including two boats and outboard motors. Hipercorig allows for about 10 m rate of penetration per shift and produces 7.5 cm cores in 2 m long core runs.

A first deployment on Lake Mondsee to initially test and modify Hipercorig recovered 64 m sediment core from glacial tills. A follow on shake-down cruise on Lake Constance served as deep-water trial and to sample so far unearthed pre-Holocene strata below about 12 m sediment depth. Coring was performed in summer 2019 in 204 m water depth, 2 km SSW of Hagnau, Germany. The site is located close to the deepest part of this basin with best possible preservation of a continuous and undisturbed depositional record. Two sediment cores of 24 and 20.5 mblf were retrieved and complemented by three 2-m-long surface cores. The uppermost 11 m of sediments consist of Holocene lacustrine clays with increasing intercalations of silt, while late Quaternary glacial sands dominate below 11 m. The piston coring device was modified to allow for penetrating these rigid sand layers, but the sands slowed down core recovery and caused core loss of ~15 cm at the end of each core run but overlapping coring was used to compensate the loss. While samples for microbiology have been taken immediately, core opening, description, and sampling will be performed at Bern University, Switzerland, in October 2019.

Currently Hipercorig receives final upgrades for safety and flexibility so that the whole system will be available from spring 2020 on for scientific coring projects on a non-for-profit base to teams with funded research projects. They will have to raise transport and operations costs as well as a maintenance fee that will serve to sustain the tool. The German Scientific Earth Probing Consortium GESEP will provide an oversight board to prioritize projects and support projects in implementation.

How to cite: Harms, U., Raschke, U., Schwalb, A., and Wittig, V.: Lake Constance sediments recovered using novel piston coring system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13070, https://doi.org/10.5194/egusphere-egu2020-13070, 2020.

Chikyu Shallow Core Program (SCORE) is a short and shallow ocean drilling program arranged by Japan Drilling Earth Science Consortium (J-DESC), Japan. SCORE provides opportunities for scientific ocean drilling test and project which can complete in a short period of time by using the ocean drilling vessel D/V Chikyu except for IODP expedition period. The title of this project is “Enigmatic recurrence pattern of Tokai earthquake in Nankai Trough, southwest Japan: the link between great earthquakes and ridge subduction”. The objective of our program is to investigate the past earthquake occurrence from a continuous sedimentary sequence at a local tectonic basin (i.e., Kanasunose Trough) in Nankai Trough. The target of this drilling program is to find an enigmatic recurrence pattern of Tokai earthquake in Nankai Trough, southwest Japan. Hydraulic Piston Coring System (HPCS) of the ocean drilling vessel (D/V) Chikyu can provide an opportunity to obtain an excellent long and continuous sedimentary record to unravel the earthquake recurrence pattern of this study area.

Expedition 912 was conducted by D/V Chikyu sailing from Shimizu to Sasebo, Japan from 4 January - 15 January 2020. The Leg 1 of Expedition 912 was cored Hole A and B in Site C9035 which are located in 34°05.7’N, 138°08.03’E with 2442 meters of water depth in the Kanasunose Trough, Tokai, Nankai Trough. The Penetration depth at site C9035 is 80.19 meters with HPCS drilled from 5 January to 8 January 2020. The thickness of Hole C9035A sediments was 9.5 m with a recovery of 105%. The thickness of cored sediments was 80.19 meters at Hole C9035B, with a recovery of 104.7%. The shipboard measurements of whole-round core samples involved X-ray CT scan and Physical properties. After splitting, the visual core description (VCD), smear slides, split surface image, Natural Remanent Magnetisation (NRM), penetration strength, and moisture and density (MAD) measurements, and Vane shear test were conducted.

The sedimentary succession is dominated by silty sediments with numerous coarse-grained (coarse silt–very fine sand) layers and some volcanic ash layers and spots. Two lithological units (Unit I and II) can be distinguished on the basis of sedimentary facies. Unit I consists of bioturbated silt and layered coarse silt–very fine sand with massive silt. Three ashes can be founded in Unit I and will provide good age control. Unit II is characterized by matrix-supported gravelly mud–muddy gravel and angular mudstone gravel. After measurements, the extended work of the recurrence intervals of seismo-turbidite in geological time will be built to stimulate the link between great earthquakes and ridge subduction.

How to cite: Hsiung, K.-H., Kanamatsu, T., Ikehara, K., Miura, I., Ashi, J., Kodaira, S., Arai, K., Okutsu, N., and Aoike, K.: Preliminary report on the sedimentary record of SCORE Site C9035 of Tokai, Nankai Trough, southwest Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4270, https://doi.org/10.5194/egusphere-egu2020-4270, 2020.

Drilling by the Ocean drilling Program (ODP Legs 104, 152, 163) and geophysical studies have inferred a widespread and strong influence by the Iceland plume on the structure of the ~2500 km long volcanic rifted margins that formed between East Greenland and NW Europe during continental breakupat  ~56-54 Ma. A persistent, but spatially much reduced impact by the plume on crustal structure is evident along the ~250 km Greenland-Iceland-Faeroe ridge (GIFR). Spreading south of the GIFR has remained comparatively stable along the Reykjanes Ridge (RR). By contrast, spreading between the GIFR and northwards to the Jan Mayen Fracture Zone (JMFZ) involved northward rift propagation (~50-25 Ma) away from the Iceland plume and into the East Greenland margin. This was paired with a northward retreat of the initial spreading axis (Aegir ridge (AER)) further to the east. Slivers of the East Greenland continental crust topped by continental plateau basalts extruded during initial breakup were torn off by this northward rift propagation, and form segments of the Jan Mayen microcontinent (JMMC). Rift propagation resulted in the formation of the Iceland Plateau (IP) underlain by anomalously thick and shallow oceanic crust. The striking asymmetry in plate kinematics and crustal structures south and north of Iceland seems associated with a less enriched mantle source feeding the spreading system north of Iceland. This suggests a potentially long-lived north-south asymmetry in the composition and dynamics of the plume that, if confirmed, will favor the existence of distinctly different mantle reservoirs rather than a mixing (entrainment) process followed by a compositional de-convolution process during decompression melting and melt distribution. IODP proposal 976-Pre will address these topics by investigating the temporal and compositional development of the crust of the IP, as well as the transition from rift propagation by the IP rift (IPR) into the present day Kolbeinsey ridge (KR). Drilling will sample 2-3 stages of four IPR propagation stages we have mapped, the transition from the IPR to KR spreading, rifting and timing of transpressive movements along the pseudo-transform zone that linked the propagating IPR to the retreating AER. One drill site hopefully will establish the stratigraphic relationship between the JMMC basalts and the East Greenland plateau basalts. Sediment cover at the drill sites will constrain subsidence history and the paleo-environmental evolution of the high-latitude north-east Atlantic and its connectivity to the global ocean.The proposed drilling addresses long-standing ocean drilling themes of continental breakup, rift propagation, mantle plume reservoirs and structure, and north Atlantic paleoceanography.

How to cite: Larsen, H. C., Blischke, A., and Brandsdóttir, B. and the IODP Proposal 976-Pre working group: Rift propagation north of Iceland: A case of asymmetric plume - rift interaction?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4219, https://doi.org/10.5194/egusphere-egu2020-4219, 2020.

Understanding past variability and forcing mechanisms of the Asian monsoon system is of key importance for better forecasting its behaviour under future global warming scenarios and how this may affect modern societies and economies. So far, knowledge about long-term monsoon variability in mainland Asia is mainly based on proxy records from Chinese speleothems, primarily recording changes of the East Asian Summer Monsoon (EASM). These records have provided evidence for orbital-scale monsoon variability, driven by Northern Hemisphere summer insolation changes, but also for centennial- to millennial-scale reductions in monsoon precipitation. These so-called Weak Monsoon Intervals (WMIs) occurred synchronously to cold intervals in the North Atlantic realm, e.g. during Heinrich Events, pointing at a close hemisphere-scale climatic teleconnection between the North Atlantic and Asia. However, the exact mechanisms that control short-term monsoon variability are still elusive. Moreover, long-term palaeomonsoon proxy records from the core zone of the Indian Summer Monsoon (ISM) are still relatively scarce compared to those from the EASM realm. To identify possible short-term changes in ISM intensity and reconstruct related hydroclimate and vegetation changes on the Indian subcontinent during the interval ~6–74 ka BP, sediments from IODP Site U1446 in the NW Bay of Bengal have been analysed. This site, being located within the reach of the Mahanadi River, is characterized by high riverine input of terrestrial organic matter and thus ideal for high-resolution analyses of pollen content and the stable hydrogen (δD) and carbon (δ¹³C) isotope composition of n-alkanes from terrestrial plant leaf waxes. Here we present preliminary results of δD and δ¹³C analyses on odd-numbered long-chain n-alkanes (n-C₂₇ to n-C₃₃,) extracted from the IODP Site U1446 sediments. These indicate several reductions in ISM precipitation during the last glacial, which occurred parallel to cold events in the North Atlantic realm, e.g. during Heinrich events H1, H2, H4, H5 and H6. In combination with pollen and alkenone-based (U^K’₃₇) sea surface temperature data from the same sediments, we aim at (1) providing a comprehensive and high-resolution reconstruction of past ISM variability and associated vegetation changes on the Indian subcontinent and (2) understanding the trigger mechanisms of centennial- to millennial-scale WMIs, particularly in relation to changes in Indian Ocean oceanography.

How to cite: Lauterbach, S., Andersen, N., Clément, C., Desprat, S., Zorzi, C., Anupama, K., Prasad, S., Oliveira, D., Blanz, T., Thirumalai, K., Clemens, S. C., Martinez, P., and Schneider, R. R.: Indian subcontinent hydroclimate and vegetation changes during the last glacial reconstructed by leaf wax stable isotope and pollen analyses on sediments from IODP Site U1446, NW Bay of Bengal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19204, https://doi.org/10.5194/egusphere-egu2020-19204, 2020.

The Mid Pleistocene Transition (MPT) was a global climatic event characterized by a drastic change in the deep thermohaline circulation during the glacial periods that resulted in more intense and longer lasting cold periods and cooler sea-surface temperature (SST). These changes might be linked to the atmospheric pCO₂ reduction which in turn led to colder atmospheric temperatures and the expansion of continental ice sheets. In the mid-latitude North Atlantic, high-resolution records documenting the MPT's impact are still limited. Thus, this study's objective is to contribute to the knowledge by reconstructing circulation changes in the subtropical gyre realm off the southwestern Iberian Margin.  We use planktonic foraminifera faunal data from Integrated Ocean Drilling Program (IODP) Site U1387 (Faro Drift, Gulf of Cadiz) to characterize centennial-scale SST variations during the interval from Marine Isotope Stage (MIS) 18 to MIS 28. The results indicate relative stable SSTs during the interglacial and interstadial periods with temperatures around 20°C during summer and 16°C during winter. During MIS 20, 22, 24, and 25 short-termed extreme cold events were recorded when winter temperatures dropped below 5°C, during late MIS 22 even close to 0°C. They mark the terminal stadial events during deglaciation and were related to increased abundance of polar planktonic foraminifera species N. pachyderma that reached values near to 80%. N. pachyderma values. Percentages of that species between 90 and 50% can be found in the polar regions near the Arctic Front and those between 50 and 5% are indicative of subarctic waters. Whereas the terminal stadial events and the first stadial phase of MIS 22 were marked by incursions of polar surface waters to the southern Iberian margin, abrupt cold events during periods of continental ice shield growth of MIS 19, 21, 25 and 28 were associated with subarctic surface waters. During the MPT, the waters off southern Iberia, therefore, experienced cooling events more extreme than during the last glacial cycle.

How to cite: Mega, A., Salgueiro, E., and Voelker, A. H. L.: Evidence for polar surface-water incursions into the Gulf of Cadiz (SW Iberia) during the Early-to-Mid Pleistocene Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2475, https://doi.org/10.5194/egusphere-egu2020-2475, 2020.

Serpentine seamounts located in the forearc region of a subduction zone setting represent an excellent natural laboratory for studying the geochemical processes acting along convergent plate margins and the associated natural hazards as well as the forearc structure and fault patterns. Active serpentinite mud volcanoes are currently restricted only to the Izu-Bonin-Mariana system, where old (presumably Cretaceous) oceanic lithosphere is subducting in the absence of an accretionary prism.

IODP Expedition 366 recovered cores from three serpentinite mud volcanoes at increasing distances from the Mariana trench (Yinazao, Fantangisña and Asùt Tesoru). Most of the material consists of serpentinite mud containing lithic clasts from the underlying forearc crust and mantle as well as from the subducting Pacific plate. A thin cover of pelagic sediments and volcanic ash deposits underlying the mud volcanos were also recovered. Recycled materials from the subducted slab are found at all three mud volcanoes and consist of metavolcanics rocks, metamorphosed pelagic sediments including cherty limestone as well as fault rocks.

Preliminary investigation of recovered sedimentary clasts from the summit of Fantangisña Seamount revealed that they contain primary calcite veins, whereas the latest veins are composed of aragonite (CaCO₃) and barite (BaSO₄).

Recovered clasts from the flank consist mainly of ultramafic rocks with various degrees of serpentinization. The serpentinite veins consist of lizardite and chrysotile, which suggests rather low temperatures of serpentinization (below 200 °C). Petrological analysis of metabasalt clasts from the same drilling hole shows changes in the mineral composition within the different intervals of the core. The composition of clinopyroxene varies between aegirine-augite and omphacite, but augite is also present. The presence of phengite with Si content of 3.5-3.8 a.p.f.u. indicates minimum pressure of 0.7 GPa at ~250 °C.

Furthermore, providing a detailed characterization of the fluids composition and transport would allow the better constraining of the tectonic and metamorphic history as well as the physical properties of the subducting Pacific Plate. Obtaining data on that point is in progress and will be presented additionally.

How to cite: Kurz, W., Miladinova, I., Del Gaudio, A. V., Piller, W., and Krenn, K.: Serpentinite mud volcanism and exhumation of fore arc- and lower plate material in the Mariana convergent margin system (IODP Expedition 366), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5452, https://doi.org/10.5194/egusphere-egu2020-5452, 2020.

The Corinth Gulf is a semi-closed active rift basin, which alternated between marine and isolated/semi-isolated conditions as sea level fluctuated with respect to basin sills during Quaternary glacial/interglacial cycles. Results from the recent IODP Expedition 381 reveal cyclic variations of 10s-100s of kyr in sedimentation rates and basin paleoenvironment. In this study we investigate the controls on stratigraphic development of the Corinth basin during the last eustatic cycle and the Holocene based on core data from the IODP Expedition 381 Site M0079. We perform a multi-proxy analysis of the upper ~200 mbsf of core covering Marine Isotope Stages (MIS) 1-5 (i.e. last 130 kyr). Our analyses include grain size and micropaleontological (foraminifera) analyses at regular intervals (~0.5 m), Computed Tomography (CT-scanning) of selected u-channels and specific microscopic work (smear slides, SEM) on targeted samples. Our results show pronounced variability in sedimentation patterns during the isolated/semi-isolated phases compared to the marine intervals. Low density, thinly bedded and laminated muds alternating with high density homogenous mud beds and occasionally sandy, organic rich beds prevail during isolated/semi-isolated conditions. In contrast, homogenous and/or highly bioturbated successions characterize the marine sequences. The transitions from marine to isolated/semi-isolated conditions and vise-versa are often associated with authigenic carbonate deposition. Fine grained sediments (sand < 10%) dominate both the marine and the isolated sequences. Nevertheless, sandy turbidites (sand > 10%) are also present and are more often observed in the isolated phases, likely associated with climatic-driven changes in erosional processes onshore. Our analysis reveals short-lived isolated/semi-isolated sub-phases within the lower marine interval corresponding to the MIS5b and MIS5d lowstands. Short marine spikes also interrupt the isolated/semi-isolated conditions of the last glacial period indicating temporary sea level rises within MIS3. Overall, the marine intervals display significant paleoenvironmental differences although they share similar sedimentary patters. In particular, we observe more diverse palaeoceanographic conditions in the MIS5 marine sub-phases compared to the MIS1, especially regarding temperature and eutrophication levels of the water column.  

How to cite: Pechlivanidou, S., Sergiou, S., Geraga, M., Gawthorpe, R., Antoniou, D., Angelopoulou, D., Ford, M., and Fabregas, N.: Controls on stratigraphic variability in a semi-closed rift basin over the Late Quaternary, Gulf of Corinth, Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11898, https://doi.org/10.5194/egusphere-egu2020-11898, 2020.

The continuous wireline core drilling of the COSC-1 borehole (Jämtland, Central Sweden) offered the unique opportunity to combine data and findings from drilling mud gas monitoring, downhole geophysical logging and drill core analysis. The COSC project aims to better understand deep orogenic processes in mountain belts in a major mid-Paleozoic environment in western Scandinavia. The 2.5 km deep fully cored borehole COSC-1 was drilled in 2014 into the lower part of the Seve Nappe Complex, characterized by a thick sequence of high-grade metamorphic rocks. Here, we present results from a combination of drill mud gas monitoring with data from geophysical logging and core analysis to identify and characterize fluid-bearing open fractures during drilling of metamorphic rocks. Geophysical downhole logging is an established technique for extracting information from the underground. Online monitoring of drilling mud gas (OLGA) is also increasingly used in scientific drilling operations, but a combined interpretation of the data sets obtained with these methods has rarely been carried out in the past. Nearly complete gas records were obtained by OLGA with three meter depth resolution from 662 m to 1709 m and six meter resolution from 1709 m to 2490 m depth (COSC-1 total depth: 2496 m) for hydrogen, methane, carbon dioxide and helium by on-line drilling mud gas monitoring. Between 662 m and approx. 1550 m, both He and CH₄ form broad peaks superimposed by several spike-like features. Zones with gas spikes coincide with high resistivity intervals identified by dual laterolog measurements and show fractures in optical drill core scans, borehole televiewer images, and visual core inspection. Therefore, we assume gas inflow through open fractures where deep/shallow resistivity ratios is greater than 1.5 imply the presence of free gas. The correlation between helium and deep/shallow resistivity ratios no longer appears at depths greater than 1550 m, probably because the formation gases are dissolved in formation fluids at higher pressure. 13 gas zones found in the depth interval 662 – 1550 m match with areas of higher resistivity and with open fractures identified by optical core logging. Below 1550 m depth, He drops significantly, whereas CH₄ remains relatively high and H₂ and CO₂ reach maximum values. The high amount of hydrogen and methane at depths below 1616 m, from where friction between the casing and the drill string was reported, imply that these gases are most certainly artificially generated at depths below 1616 m and at least partly of artificial origin at shallower depths. Comparison between OLGA data and resistivity downhole logging data can help to estimate degassing depths: at depths where OLGA identified formation gases, concurrent high resistivity would be diagnostic for free gas, whereas low resistivity would imply gases dissolved in saline formation fluids.

How to cite: Pierdominici, S., Wiersberg, T., Lorenz, H., Almqvist, B., and Klonowska, I. and the COSC Science Team: Integration of drilling mud gas monitoring, downhole geophysical logging and drill core analysis identifies gas inflow zones in borehole COSC-1, Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3407, https://doi.org/10.5194/egusphere-egu2020-3407, 2020.

Reconstructing the history of continental records covering the glacial-interglacial cycles was the main objective of the ICDP Lake Junín drilling project. Located at 4000 m above sea level, Lake Junín is characterized by a thick sediment package (>125 m) deposited with a sedimentation rate of 14-15 cm/kyr. In fact, the lake predates the maximum extent of glaciation, and is in a geomorphic position to record the waxing and waning of glaciers in the nearby Cordillera. Drilling was performed in 2015 at three sites and a suite of downhole logging measurements were applied. Downhole logging measurements were used to recognize the glacial and interglacial cycles, to reconstruct an age–depth model, to estimate sedimentation rates and to identify electrofacies. Initially, we investigate the consistency of cyclic sediment behavior and see that the interval from ~30-90 m shows a rather stable cyclicity with a wavelength of ~10 m. Natural and spectral gamma ray data were used for cyclostratigraphic analysis, and the astronomical spectral misfit (ASM) method was used to reconstruct the sedimentation rate. The results indicate a sedimentation rate of about 5-20 cm/kyr in the Lake Junín record. Furthermore, the TimeOpt method was applied to test for a fit of precession amplitude with eccentricity; it results in an average sedimentation rate of 15 cm/kyr. Both ASM and TimeOpt are astronomical testing approaches for untuned stratigraphic data in the depth domain that comprehensively evaluate a range of plausible time scales for the deposition history. This method suggests a good fit of the precession amplitude and an eccentricity filter when applying an average sedimentation rate of 14-15 cm/kyr. Based on these information on sedimentation rate, we establish a correlation of the spectral gamma ray data to the LR04 benthic isotope stack. In addition, the downhole logging data were used for cluster analysis to construct a lithological profile, called the electrofacies log.  Three major groups (carbonate-silt, peat and silt) have been identified by spectrum gamma ray, magnetic susceptibility, and p-wave velocity logs. With this method we are able to attribute the lithology in correspondence of core gaps. Finally, the properties of the clusters are analyzed and converted into lithological units according to the lithological information from the visual core description or mineralogical analysis or core material. To achieve this, 68 samples were taken in total from two core runs, in order to compare and characterize the minerals in the lake sediments at different depths. The mineralogical analyses performed by X-ray diffraction (XRD) show quartz, calcite, feldspar and clay minerals. The clay size fraction (< 2 micron) contains illite, smectite and kaolinite in different amounts. Linking the abundance and the lack of clay minerals in core samples with the downhole logging data, a relationship between geological history of the lake and climate change processes can be recognized. Consequently, the different mineralogical composition of the sediments, especially the presence or absence of smectite in the clay bulk, reflects a glacial/interglacial climate cyclicity.

How to cite: Schleicher, A., Pierdominici, S., Zeeden, C., Kück, J., Rodbell, D., and Abbott, M.: Investigating glacial/interglacial cyclicity from downhole logging data and mineralogical composition: an example from the ICDP drilling project Lake Junín, Peru, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3891, https://doi.org/10.5194/egusphere-egu2020-3891, 2020.

Chicxulub crater was formed ~66 Ma ago by an asteroid impact at the Cretaceous/Paleogene (K/Pg) boundary on the Yucatan carbonate platform in the southern Gulf of Mexico. The crater is the youngest and best preserved of the three large impact basins, with a ~200 km diameter and multi-ring and peak ring morphology. The crater, covered by post-impact carbonate sediments with thickness up to ~1.1 km, has been investigated by geophysical studies and drilling programs. Initial drilling in Yucatan was carried out by the Pemex oil company, followed by the National University UNAM Chicxulub program, the ICDP Yaxcopoil-1 project and the IODP-ICDP Expedition 364 marine drilling. Here, results of combined paleomagnetic, rock magnetic, petrographic and geochemical studies are used to characterize the sequence and constrain the unit’s emplacement and crater formation. We analyze core samples of suevitic breccias and Paleogene carbonates from the Yaxcopoil-1 and Santa Elena boreholes drilled in the southern sector, inside and to the south of the crater rim marked by the ring of cenotes.  Magnetic hysteresis, low-field susceptibility and coercitivity analyses indicate that main carriers are titanomagnetites and magnetite. Mineralogical and magnetic properties indicate effects of hydrothermal alteration, associated with the high temperature system generated by the impact. Higher coercitivity minerals are also observed in some samples. In the carbonate sections, hydrothermal effects as marked by the geochemical logs decrease upwards from the breccia-carbonate contact. Alternating field and thermal demagnetization is used to investigate the magnetization vector composition and isolate the characteristic remanent components. Magnetic polarities defined from the inclination data show a sequence of reverse to normal, which correlate to polarity chrons 29r to 26r, with impact occurring within 29r chron.  The correlations of the magnetostratigraphy and stable isotopes indicate a hiatus at the basal Paleocene section. In Santa Elena cores, d¹³C values range from 1.2 to 3.5%₀ and d¹⁸O values range from -1.4 to -4.8%_0, with variation trends correlating with the marine carbon and oxygen isotope records for the late Maastrichtian and early Paleocene. The positive carbon isotopes indicate high productivity after the K/Pg extinction event, while the oxygen isotope values are more negative reflecting regional and local effects. Silica contents decrease from high in the suevites to low values in carbonates showing higher variability and then increased contents at the Paleocene-Eocene Thermal Maximum (PETM). The geochemical trends correlate in other elements including iron, titanium, potassium and aluminum that record impact-induced hydrothermal effects and possibly changing depositional conditions. Ca shows an opposite trend, with lower values in the upper suevitic breccias, higher values in the Paleocene carbonates and lower values in the PETM.

How to cite: Urrutia-Fucugauchi, J., Perez-Cruz, L., Escobar-Sanchez, E., Velasco-Villarreal, M., and Garcia-Garnica, E.: Rock Magnetic and Magnetostratigraphic Study of Chicxulub Crater Impact Breccias and Post-Impact Carbonates in the Yaxcopoil-1 and Santa Elena Boreholes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19628, https://doi.org/10.5194/egusphere-egu2020-19628, 2020.

Kerguelen Plateau (KP), one of the world’s largest Large Igneous Provinces, is located in a key region in the southern Indian Ocean. Its complex topography has a strong influence on pathways of water masses within the Antarctic Circumpolar Current (ACC) and the Antarctic Bottom Water (AABW). Thick sediment packages deposited on top and around KP are a high-fidelity recorders of significant modifications in pathways and intensities of water masses flowing across the KP during the Cenozoic. Already the previously ODP spot cored sedimentary sequences demonstrated their outstanding potential as a far-field monitor for the evolution of the Antarctic Ice Sheet, for the climate variability in the Warmhouse World of the middle to late Eocene, for changes in ocean circulation, and for migration of the Polar Frontal System. Here we propose to revisited KP and recover a complete, multiple-hole drilled, carbonate rich sedimentary successions from Labuan and Ragatt Basin area by an IODP Expedition. Only high-quality drilled, undisturbed new material will allow studying the interaction of climatic and tectonic changes of the last 66 million years and provide important information on the formation and dynamics of the Antarctic ice sheet due to the unique location of the KP.

How to cite: Westerhold, T. and Uenzelmann-Neben, G.: Kerguelen Plateau Drift Deposits: outstanding high-resolution chronicle of Cenozoic climatic and oceanographic changes in the southern Indian Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3121, https://doi.org/10.5194/egusphere-egu2020-3121, 2020.

The formation of a solid-state material from solution is a ubiquitous process of fundamental importance not only for synthesis in solid-state chemistry but for a wide range of disciplines such as geosciences and biology. However, established classical crystallization theories fall short in explaining the outcome of crystallization and mineralization processes in complex environments, such as in biomineralizing organisms or geochemical and industrial settings.  The misfit between classical textbook knowledge and the plurality of conflicting experimental evidence facilitated the advent of an array of new crystallization concepts. These so-called nonclassical crystallization processes are fuelled by the attachment of multiatomic assemblies rather than by attachment of single ions drive crystal formation. Some of these models, such as oriented attachment, were unequivocally backed by experimental evidence and thus accepted by the science community. Other models have encountered distinct resistance from peers. At the centre of this intense dispute, we find the calcium carbonate system, which is of crucial importance for a range of disciplines. For this system, in particular, the existence of prenucleation clusters in the form of dynamically ordered liquid-like polyoxoanions (DOLLOP) has been suggested, and it has been claimed that nonclassical nucleation processes take place. However several groups have challenged this claim, claiming an entirely classical crystallization behaviour

Based on our results, we will draw a different picture of calcium carbonate formation. We show that the issues with this very systems root in its solute chemistry and the fact that this renders a calcium carbonate solution into a multicomponent system. We show liquid-liquid phase separation of near-neutral calcium carbonate solutions along with the first ultrastructural model of amorphous calcium carbonate (ACC). This findings give insight into the formation mechanisms of calcium carbonate under kinetically controlled conditions. Our findings further demonstrate that the formation of a liquid-condensed mineral precursor phase is not solely a “quirk of the peculiar calcium carbonate system” but a general phenomenon: it is an early stage precursor in the formation pathway of calcium carbonate under geo- and biochemical relevant conditions. Moreover, we show that this unexpected demixing behaviour is widespread, many inorganic components go through spinodal decomposition, when the reaction conditions are kinetically controlled and the solution chemistry disadvantage burst nucleation. Our data suggest that it is not the misconception and oversimplification of classical theories but our oversimplification of the solution chemistry which causes the current dispute on classical vs nonclassical nucleation of inorganic compounds. Currently, we see no need for invoking “non-classical” notions of nucleation since our exceptional observations can entirely be explained by established physicochemical concepts apart from CNT. Our results raise the awareness that a supramolecular solution and coordination chemistry provides the key to a thorough understanding of the genesis of inorganic solids under kinetically controlled conditions.

How to cite: Wolf, S.: From solutes to solids: towards a supramolecular view on mineralization processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21861, https://doi.org/10.5194/egusphere-egu2020-21861, 2020.

Directly west of the San Rafael Swell on the Colorado Plateau in the western U.S., the Jurassic Entrada Sandstone is intruded by a ~2 km long mafic dike. The dike is Miocene; however, the area is also crosscut by Laramide (~50Ma) clusters of deformation bands that are up 500 m long and up to ~3 m wide. The mafic intrusions infused the area with fluids that bleached the red sandstone directly surrounding the dike. On one side of the dike, the bleached area terminates at an adjacent deformation band set ~475 m south of the dike. Field observations suggest that the dike acted as a baffle preventing fluids from migrating further into the sandstone. Spheroidal calcite and iron (oxyhydr)oxide concretions are present in the bleached host rock, although calcite concretions (1-3 cm diameter) are present throughout the area on both sides of the deformation bands and in both red and white host rock. Iron (oxyhydr)oxide concretions (1-5 cm diameter) are limited to the uppermost bleached section between the dike and the deformation band set. Some iron concretions have solid interiors, and some have well-cemented rinds with interiors depleted of cement. Additionally, some iron concretions are nucleated on individual deformation bands that are ~2 mm wide and iron (oxyhydr)oxide cemented joint faces are also present. Thermochemical modeling shows the infiltrating Miocene fluids were CO₂-bearing, but near neutral pH. The restricted location of the iron (oxyhydr)oxide concretions and relation to the calcite concretions suggest that stagnation of fluid is needed for spheroidal iron oxyhydroxide concretion formation. Calcite concretion nucleation and growth may be quicker resulting in more widespread occurrences, and/or may have preceded the Miocene fluids that infiltrated the unit. The evidence presented here shows that recently proposed models calling for calcite concretion precursors and acidic fluids for iron (oxyhydr)oxide concretion formation may not be correct.

How to cite: Potter-McIntyre, S., Filiberto, J., Schwenzer, S., Crandall, J., Perl, S., and Baharier, B.: New insight into spheroidal iron (oxyhydr)oxide concretion formation models: Diagenetic concretion nucleation associated with neutral fluids from a mafic intrusion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2104, https://doi.org/10.5194/egusphere-egu2020-2104, 2020.

In the semi-arid region south of Sulaimani city, paleosols can be found. The genesis of these paleosols needs to be elucidated. Here, we investigated a section of an Oligocene paleosol from that region. The section is about 7m thick with lower, middle and upper horizons, which consisted of partially weathered dolomitic limestone; conglomerate or lithified pebbly paleosol; and sandy-silty claystone or lithified clayey paleosol, respectively. These horizons were studied mineralogically and stratigraphically using X-ray diffraction, scanning electron microscopy, Simultaneous Thermal Analysis (STA) and granulometric analysis. Palygorskite content was higher in the conglomerate (lithified gravely paleosol) and in the partially weathered dolomitic limestone than in clayey paleosol.

Palygorskite is a trace mineral that allows to estimate climatic conditions during soil genesis. In hand specimen, palygorskite occurs as green patches of crystalline coating that covers pores and cavities on limestone and dolostone. Under scanning electron microscope, it appears as linear and fibrous loose bundles that occupy the interstice between the dolomite crystals and is mainly associated with dolostone and limestone facies.

We thus conclude that the climate was arid, and that the terrestrial land cover in this part of the Oligocene Basin in Northern Iraq was limestone and dolostone.

On this land, soil genesis and intermittent stream and sheet erosion was occurring during the entire Oligocene and it is well known, stratigraphically, as Oligocene Unconformity.

The possible origin of the palygorskite was the development during Oligocene by upward accumulation under hydrothermal condition in partially high weathered dolomitic limestone of Pila Spi formation during burial. Palygorskite occurs in marine, lacustrine and soil environments. Limited occurrences are associated with hydrothermal activity, in both marine and continental environments. Palygorskite-containing soils are limited almost exclusively to arid and semiarid areas of the world and are rather unstable in humid conditions.

The present paleosol was developed on Oligocene terrestrial land that bordered the sea covering Middle and Southern Iraq. Due to non-deposition weathering and mass wasting, calcareous gravely soil (limestone conglomerate) was generated. Sandy and clay soil were developed on the terrestrial land which stratigraphically formed an unconformity. This land was covered by water of a closed lagoon. Limestones are deposited as Lower Fars Formation.

These occurrences are associated with aquatic conditions characterized by alkaline solutions with high activities of Si and Mg. The most common setting for lacustrine palygorskite genesis are playa deposits, ancient lacustrine terraces, or closed-basin deposits of other types. While traces of palygorskite can be identified in a wide variety of soils, significant amounts of the pedogenically formed mineral are commonly associated with one specific situation of soil genesis like soils have been affected by fluctuating ground water, soil morphology that includes distinct and sharp textual transitions. This groups includes many paleosols. Most of these Paleosols are non-saline or only slightly saline.

How to cite: Mentler, A., Khanaqa, P., Karim, K., Ottner, F., Schomakers, J., Keiblinger, K., and Kral, R.: Palygorskite in a Paleosol from Zagros mountain belt, NE Iraq, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19949, https://doi.org/10.5194/egusphere-egu2020-19949, 2020.

Spectroscopy based methods have proven great potential in efficient, non-invasive material characterization. Recording the material-specific optical properties delivers instant information on the composition of an investigated sample surface without chemical sample preparation and may be operated in spatially continuous mode. In minerals, laser-induced fluorescence (LiF) provides a promising method to address the challenges of robust and efficient rare-earth element (REE) detection. The method is based on the characteristic electronic transitions within the incompletely filled f-shell of REE. The corresponding emission shows distinct features (spectral fingerprints) in the visible and near-infrared (VNIR) range of the electromagnetic spectrum that allow to distinguish between individual REE and mineral matrix luminescence. Only REE with completely filled or empty f-orbitals miss characteristic luminescence (i.e. Y³⁺, Sc³⁺, La³⁺, Lu³⁺), while the emissions of Gd³⁺ lie at lower wavelengths than the observed VNIR range.

We test the suitability of LiF in applications of REE identification by (1) building a spectral LiF library from a sample set of luminescent REE phosphates and (2) evaluating observed emissions in samples of non-luminescent REE, and (3) comparing indicated REE cross-contamination to results of neutron activation analysis (NAA). As samples, we use the Smithsonian REE phosphate standards for electron microprobe analysis. The synthetic material delivers a simple, well-defined host composition, is well investigated and NAA results are available on additional trace REE concentration resulting from the material production procedure. The trace REE concentrations are at the order of 10^-4 given in mass fraction. We employ laser-induced fluorescence at three commonly used laser wavelengths (325 nm, 442 nm, 532 nm) to acquire our REE sample spectra and record LiF signals in the visible to near-infrared spectral range (350 – 1080 nm).

The comparison of spectra from non-luminescent REE phosphates shows clear similarities in emission patterns that can be assigned to specific luminescent REE using the spectral LiF library. Our results demonstrate the suitability of LIF for REE detection along with the benefits of selective element excitation and highlight the high sensitivity of the LiF method. The detected emissions in the non-luminescent samples indicate a detection limit below mass fractions of 10^-4, when compared to NAA results, but also show that not all REE are equally responsive. Here, the co-existence of REE with complex interactions such as charge transfer contributes to the observed emission pattern. Adding to the spectral LiF library data and expanding investigations to further mineral hosts will facilitate new applications of LIF for REE analysis in natural samples and its implementation in raw material exploration.

How to cite: Fuchs, M. C., Beyer, J., Lorenz, S., Sharma, S. K., Renno, A. D., Heitmann, J., and Gloaguen, R.: Laser-induced fluorescence (LiF) spectroscopy for detecting REE cross-contaminations in the Smithsonian rare-earth element phosphate standards , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11006, https://doi.org/10.5194/egusphere-egu2020-11006, 2020.

The diameter of framboidal pyrites was widely used as a measure of redox condition in modern and ancient sedimentary environments, the proposed critical values of average size and standard deviation of framboids are about 8μm and 3μm respectively. However, a few reports proposed that the exceptionally large size and standard deviation of framboidal pyrites in cored sediments from northeastern South China Sea is closely related to the anaerobic oxidation of methane (AOM) processes mainly dominated in sulfate-methane transition zones (SMTZ). Here we investigate the occurrence of framboidal pyrites in two cored sediments of sites SC-W02B-2017 and SC-W03B-2017 at Shenhu area during the first offshore gas hydrate production test in northern South China Sea. Combined with the statistics of size and standard deviation of framboidal pyrites, the relative concentrations and sulfur isotopic compositions of bulk pyrites, we verified that the AOM could enhance the framboidal pyrite formation. Our data show that both the size and the standard deviation of framboidal pyrite present an unusual positive excursion in cored sediment column. By interpreting the coupling occurrence of positive excursions both pyrite concentrations and sulfur isotopes, four main paleo-sulfate-methane transition zones (Paleo-SMTZ) are roughly recognized in depths around 50 meter below seafloor (mbsf), 90-100 mbsf, 135-225 mbsf and 180 mbsf, where unusual strong AOM and unusual methane releases might happened. The morphology shows most of the pyrite framboids occur in framboidal cluster with a rod-like, irregular block shape and secondary overgrowth. The size of pyrite framboids in site W02B ranges from 8.1μm to 40.1μm with maximal about 40.1μm and in site W03B from 8.6μm to 25.3μm with maximal about 101.2μm (n=2686 from 13 samples). Our data show the average size and the standard deviation of pyrite framboids are more than 20μm and 3.0μm respectively, and the higher δ³⁴S value and larger size of framboid mainly occur near the intervals of paleo-SMTZs in marine sediment columns. Therefore, we propose again that the enhancing AOM in SMTZs could flourish the growth of pyrite framboids and enlarge the standard deviation of framboidal size, which might be implication for more precise interpretation of redox condition of sedimentary environments using framboidal pyrite diameter.

How to cite: Wang, J. and Wei, Q.: Framboidal pyrites flourished in sulfate-methane transition zones of cored sediments in the northern South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3979, https://doi.org/10.5194/egusphere-egu2020-3979, 2020.

The abundance and isotopic content of boron in carbonate biominerals provide our best records of ocean carbon chemistry and pH, which have proved instrumental in studying past episodes of CO₂-induced climate change. The boron proxies are based on the theory that carbonates solely incorporate B(OH)₄^- in proportion to seawater B(OH)₄^-/HCO₃^- or B(OH)₄^-/CO₃^2-, capturing both the state of the ocean C system and the pH-dependent isotopic composition of B(OH)4-. However, models of biomineralisation invoke significant modification of internal carbon chemistry to facilitate calcification, and substantial proton export has been observed during carbonate formation. The pH, carbon and boron chemistry at the site of calcification cannot be the same as that of external seawater. How, then, do biominerals appear to record seawater B(OH)₄^-? While unanswered, this question raises serious problems for our interpretation and use of the B proxies.

We explore this question using a quantitative model of B transport and incorporation in biomineralisation. Three key fluxes dominate biomineral formation: CaCO₃ precipitation, the exchange of seawater with the external environment, and ion transport across membranes by diffusion or active pumping. By reducing the problem to the balance between these three key fluxes, it is possible to explore a wide range of biomineralisation scenarios with minimally restrictive assumptions. Within this framework, we consider both the transport of B(OH)₄^-, and the transport and passive diffusion of membrane-permeable B(OH)₃, allowing us to explore a comprehensive range of candidate biomineralisation scenarios and B transport processes.

By explicitly including the independent transport of both B species, our model offers two key insights into the mechanisms behind the boron proxies and biomineralisation:

1. We identify biomineralisation mechanisms that allow B geochemistry to record external seawater conditions, despite the modified chemistry at the calcification site.

2. We constrain the dynamics of the calcification environment (e.g. ‘closed’ vs. ‘open’ or Rayleigh- vs. transport-dominated system) by inverting the model to consider paired B/Ca and δ¹¹B data, offering key new constraints on ion transport processes in biomineralisation.

How to cite: Branson, O. and Gagnon, A.: Boron proxies and biomineralisation: the possible, the impossible and the likely., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21988, https://doi.org/10.5194/egusphere-egu2020-21988, 2020.

Despite being some of the largest bio-constructions on the planet, coral reefs are made by many millions of cm- to mm-sized polyps of Scleractinian corals. Calcification occurs in a micron sized space sandwiched between the coral animal and the existing skeleton, known as the extra cellular medium (ECM). The coral animal has a tight control on the carbonate system in this space through deploying enzymatic pumps (e.g. Ca-ATPase) and secreting acidic-rich proteins. Tracking the state of the carbonate system in the ECM is therefore key to forming a mechanistic understanding of how environmental change, such as ocean acidification, influences skeletal formation and ultimately the growth and resilience of these important ecosystems.

Traditional means to examine ECM composition is through the use of micro-electrodes. While these approaches have revealed many key insights they are, by their nature, invasive.  They also only provide snap shots of information for corals grown in the laboratory. The boron isotopic composition of the coral skeleton and its boron content (expressed as B/Ca ratio) have recently emerged as a viable alternative approach to fully characterise the carbonate system in the ECM.  However, most studies employ bulk sampling techniques which require averaging across both structural elements of the coral skeleton and many months to years of growth. Laser ablation MC-ICP-MS approaches are now available as an alternative sampling protocol (e.g. Standish et al. 2019), and along with B/Ca (and other trace element) measurements this not only allows a reconstruction of the full carbonate system of the ECM from an analysis of the skeleton of any coral (cultured or wild) at unprecedented spatial and temporal resolution, but it also allows an examination of the influence of the carbonate system in the ECM on trace element incorporation. 

Here we present boron isotope and trace element analyses of several tropical, reef-building, corals to examine the nature and magnitude of fine scale variation in ECM composition.  By studying corals from locations where external seawater is well known we also gain insights into trace element incorporation and whether external seawater pH can be accurately reconstructed from the boron-based proxies at weekly (or better) resolution. 

Standish, C.D., Chalk, T.B., Babila, T.L., Milton, J.A., Palmer, M.R., Foster, G.L. (2019) The effect of matrix interferences in situ boron isotope analysis by laser ablation MC-ICP-MS, Rapid Communications in Mass Spectrometry 33: 959–968 https://doi.org/10.1002/rcm.8432

How to cite: Foster, G. L., Chalk, T. B., and Standish, C. D.: Boron isotope analysis of coral skeletons by laser ablation MC-ICP-MS: new insights into calcification and environmental reconstruction at high temporal resolution , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8202, https://doi.org/10.5194/egusphere-egu2020-8202, 2020.

A widespread phenomenon in biogenic and inorganic carbonates that are formed out of isotopic equilibrium is a nearly ubiquitous co-variation (slope) of carbon vs. oxygen isotopes, in e.g., speleothem and cryogenic carbonates, shells and skeletons of foraminifera, corals etc. For proxy calibrations, it is critical to understand such isotope variations (often labeled kinetic or vital effects) in proxies widely used for paleo-reconstructions. Given that this phenomenon is observed in inorganic carbonates and biogenic carbonates across different phyla suggest a common underlying mechanism, possibly independent of biological controls, that is, likely of inorganic origin. Here we present results from laboratory experiments on synthetic carbonate precipitation to constrain the kinetic isotope fractionation factor (KFF) of carbon and oxygen during CO2 hydration. We used an experimental setup similar to that of an earlier study but with important modifications and tight temperature and pH control. The average d13C and d18O values of our carbonate samples (BaCO3) produced at 25 deg C and pH = 8.0 (NBS) are -29.7 +- 0.71 per mil (VPDB) and 18.8 +- 0.56 per mil (VSMOW), respectively. From the isotope data, we calculate our experimental 13KFF and 18KFF, which refer to the 13C/12C and 18O/16O fractionation between CO2(g) and BaCO3, where the d13C and d18O values of CO2(g) were calculated using known equilibrium fractionation factors. Our results show that our KFFs are the largest values compared to previously reported experimental KFFs (except for one study), suggesting that our values are closest to the full isotopic disequilibrium during CO2 hydration. Based on our KFFs, we will present the expected slope of carbon vs. oxygen isotopic disequilibrium from kinetic effects during CO2 hydration. We will also discuss the expected slope from equilibrium effects of solution pH on oxygen isotopes. Comparison with field and culture data will reveal the origin of the slope of carbon vs. oxygen isotopic disequilibrium in biogenic and inorganic carbonates.

How to cite: Zeebe, R., Yumol, L., and Uchikawa, J.: Solution to an enigma: Explaining the slope of carbon vs. oxygen isotopic disequilibrium in biogenic and inorganic carbonates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10573, https://doi.org/10.5194/egusphere-egu2020-10573, 2020.

The Mg/Ca paleotemperature proxy in planktic foraminifera is one of the most widely-used proxies for sea surface temperature. However, this ratio is not constant throughout the test, varying systematically by several fold independent of temperature between faster and slower growing diurnal bands. This phenomenon has yet to be explained mechanistically, however, changing calcification rates may be a contributing factor. Observing the relationship between calcification rate and trace metal incorporation for multiple proxies at the scale of this banding will allow us to better understand the contribution of kinetic effects to heterogeneity. In this study, we examine Me/Ca ratios on a diurnal cycle in Orbulina universa, utilizing a novel approach based on multiple isotopic spikes that allows us to measure Sr/Ca, Li/Ca and Mg/Ca with the precision of isotope dilution while still maintaining the time resolution of microanalytical techniques. Using independently measured growth rates derived from NanoSIMS measurements of diurnal Mg/Ca heterogeneity, we examine the effect of crystal growth rate on foraminiferal Sr/Ca and Li/Ca.  We observe that Sr/Ca ratios in foraminifera are ~3% higher during the night than during the day, which initially appears opposite to the expected signal based on growth rate. However, we also observe a positive correlation between Sr and Mg in foraminiferal calcite, which falls on the same mineralogical line as the Sr/Ca and Mg/Ca of other biogenic and inorganic calcites. We attribute offsets in calcite composition from this mineralogical relationship to kinetics. Interpreted within that framework, day Sr/Ca ratios appear more affected by kinetics than night Sr/Ca ratios, which is consistent with observed calcification rates. The difference between any given data point and the mineralogical line can be explained by kinetic processes, and correlates with oceanographic properties in cultured foraminifera, which could help separate temperature from growth rate effects in the paleorecord.

How to cite: Bonnin, E., Spero, H., and Gagnon, A.: Testing the effect of crystal growth rate on foraminiferal calcite microchemistry using Sr/Ca of individual day/night bands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13960, https://doi.org/10.5194/egusphere-egu2020-13960, 2020.

Phytoplankton is one of the most important producers of oxygen, and plays an important role in the export of large amounts of carbon to the deeper ocean. Since phytoplankton is also the basis of most food webs in the ocean, understanding the dynamic system of phytoplankton is a crucial part to understand past carbon- and nutrient cycles and paleoclimatic changes. The export of nutrients is also an important factor impacting cold-water coral (CWC) reefs and may play a role in controlling their distribution. Here we present laser ablation inductively coupled mass spectrometer (LA-ICP-MS) Element/Ca measurements from Acesta excavata, a file clam, often associated with cold-water coral reefs along the European continental margin. Environmental parameters were recorded with lander systems directly deployed in the CWC reefs, which allows us to compare our geochemical data to in-situ ocean data.

Our results reveal, that Ba/Ca ratios show stable baseline values with intermittent sharp peaks. The location of these peaks in between major growth lines and temperature reconstructions with Mg/Sr ratios (Schleinkofer et al., submitted) show that these peaks occur during Winter and are repeatable between samples from the same location. This indicates a strong external forcing mechanism and allows cross-dating of different bivalve shells. While the occurrence of Ba/Ca peaks correlates with phytoplankton maxima, the absolute Ba/Ca ratio does not correlate with the phytoplankton abundance.

Mn/Ca ratios show similar trends as Ba/Ca ratios but the peaks are phase shifted and occur slightly delayed. These peaks could be triggered by decreasing oxygen concentrations in the water caused by the decomposition of organic material.

As A. excavata does not show easily distinguishable growth lines under the light microscope despite of Mutvei staining or fluorescence microscopy, we hypothesize that P/Ca ratios might be usable to locate highly phosphorylated shell areas that usually correlate with major growth lines. P/Ca ratios show no perceivable features in the vicinity of major growth lines. Instead we recognize that Ba/Ca peaks follow a minimum in P/Ca which is possibly caused by the uptake of phosphor by plankton.

These results suggest that A. excavata have potential as a promising tool for high resolution paleoenvironmental reconstructions of both intermediate and overlying surface water masses.

References

Schleinkofer N, Raddatz J, Evans D, Gerdes A, Flögel S, Voigt S, et al. Elemental to calcium ratios in the marine bivalve Acesta excavata: an archive for high-resolution paleoceanographic reconstructions of intermediate water masses. PLoS One. Submitted

How to cite: Schleinkofer, N., Raddatz, J., Evans, D., Gerdes, A., Voigt, S., and Wisshak, M.: Ba/Ca, P/Ca, Li/Ca and Mn/Ca ratios in the deep-sea bivalve Acesta excavata: Valuable tools to reconstruct plankton dynamics in cold-water coral ecosystems?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4724, https://doi.org/10.5194/egusphere-egu2020-4724, 2020.

The Cenozoic period encompasses the last transition from the “greenhouse” climate of the late Early Eocene (~50 Ma) to our modern “icehouse” climate with its much lower CO₂ levels, significant polar glaciation and major sea level drop. The Eocene-Oligocene transition (EOT), that marks the first major ice-sheet build-up on Antarctica, has been extensively studied as it represents the entrance into an icehouse mode. Identification of this major step of Antarctic ice-sheet build-up strongly relies on δ¹⁸O and Mg/Ca benthic foraminifera records from ODP / DSDP sites. By contrast, few records currently exist from coastal environments despite the presence of abundant fossil archives, like bivalve shells. Yet palaeoenvironmental records from these peculiar coastal sites could bring information on how they react to global climate changes and help to further understand the behavior of our climate system. In this study, we applied a multi-proxy strategy coupling δ¹⁸O, δ¹³C, clumped isotopes (Δ₄₇), strontium isotopes (⁸⁷Sr/⁸⁶Sr) analyses on aragonitic and calcitic bivalves and sediments recovered from the Isle of Wight (London-Paris Basin, Northeastern Atlantic Ocean) to provide additional constrain on environmental changes in this region across the Eocene-Oligocene Transition (~37.8–33 Ma).

Our new coupled δ¹⁸O and Δ₄₇ dataset highlights a marked decrease in local seawater temperatures (~ 8°C) coupled to a drop in local seawater δ¹⁸O, likely linked to the sea level drop associated with ice-cap formation and an evolution toward more proximal, brackish environment in this region (that is apparent from sediment facies evolution). We estimate the salinity decrease recorded at the local scale from the Eocene to the Oligocene as reaching about 6 PSU, from 31 to 25 PSU. Strontium isotope analyses of the bivalves support this interpretation, showing values close to that of seawater up to the EOT but a marked deviation from contemporaneous global seawater ⁸⁷Sr/⁸⁶Sr values toward more radiogenic values afterward. This positive deviation is in agreement with an evolution toward more proximal environments, subjected to larger freshwater inputs.

How to cite: Briard, J., de Rafélis, M., Vennin, E., Daëron, M., Chavagnac, V., Emmanuel, L., Merle, D., and Pucéat, E.: Paleotemperature and paleosalinity evolution across Eocene-Oligocene Transition in North Atlantic Ocean: Insights from geochemical analysis of bivalve shells., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18358, https://doi.org/10.5194/egusphere-egu2020-18358, 2020.

Zinc (Zn) is an important bioessential trace element. Its distribution in the modern oceans reflects a combination of biological uptake, remineralization and the physical ocean circulation. Furthermore, the partitioning behaviour of Zn (D_Zn) and its isotopes (δ⁶⁶Zn) in carbonates has been linked to ambient seawater carbonate chemistry [1-3].

Development of Zn isotopes in carbonates as a palaeoceanographic tool has been hampered by the high concentrations of Zn in contaminating material, such as lithogenic or authigenic (e.g. Fe-Mn oxide) phases. However, deep-sea corals are large enough to be subjected to aggressive physical and chemical cleaning, enabling effective removal of contaminating phases. They also have several other advantages over traditional palaeoclimate archives, including the ability to assign precise absolute ages to individual specimens based on uranium-series dating [4].

Here we present Zn/Ca and δ⁶⁶Zn data for a suite of modern and recent (<1000 yr) deep sea corals from six ocean regions spanning the far North Atlantic to the Tasman Sea. We observe what appears to be species-specific Zn partitioning behaviour, but no clear links between D_Zn or coral δ⁶⁶Zn and ambient seawater carbonate chemistry. Overall, there is good agreement between measured or best-guess modern seawater δ⁶⁶Zn and coral aragonite δ⁶⁶Zn values, suggesting that corals of species Desmophyllum dianthus and genus Caryophyllia do not significantly fractionate Zn isotopes during calcification. Deep sea corals may thus provide a useful archive of the past ocean Zn isotope composition and its spatial variability.

[1] Marchitto T. M., Curry W. B. and Oppo D. W. (2000). Paleoceanography 15, 299–306. 
[2] van Dijk, I., de Nooijer, L. J., Wolthers, M., & Reichart, G. J. (2017). Geochimica et Cosmochimica Acta 197, 263-277. 
[3] Mavromatis, V., González, A. G., Dietzel, M., & Schott, J. (2019). Geochimica et Cosmochimica Acta 244, 99-112. 
[4] Robinson, L. F., Adkins, J. F., Frank, N..., & van de Flierdt, T. (2014), DSR Part II 99, 184-198.

How to cite: Little, S., van De Flierdt, T., Wilson, D., Rehkämper, M., Adkins, J., and Robinson, L.: Zn isotopes in deep sea corals: a useful palaeoceanographic archive? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7732, https://doi.org/10.5194/egusphere-egu2020-7732, 2020.

The chemical composition of foraminiferal calcite is widely used for studying past environmental conditions and biogeochemistry. However, high rate of microbial-derived organic matter degradation and abundant dissolved metal sources in sediment and pore waters may impede the application of paleoenvironmental proxies due to formation of secondary carbonates on the outside and/or inside of foraminiferal tests. Secondary carbonate precipitation severely alters the foraminiferal geochemistry and can be difficult to eliminate through standard cleaning procedures for foraminiferal trace element analyses. Here we present results of the mineral composition and formation sequence of diagenetic coatings on the tests of foraminifera formed under extreme anoxic conditions in the Baltic Sea deepest basin (the Landsort Deep, IODP Exp. 347, Site M0063), as well as changing trace element concentrations of authigenic carbonates on the test on a millennial time-scale. The focus is on the diagenetic carbonates present on the tests of the low-oxygen tolerant benthic foraminiferal species Elphidium selseyensis and Elphidium clavatum. We applied geochemical and imaging methods by using scanning electron microscope imaging (SEM) and energy dispersive spectroscopy (EDS), synchrotron-based x-ray fluorescence microscopy (nano-XRF), RAMAN spectroscopy and laser ablation (LA)-ICP-MS, in order to ascertain the sedimentary diagenetic processes, and the foraminiferal authigenic mineral formation sequence. The authigenic carbonates were enriched in Mg, Mn, Fe and Ba, depending on the redox environmental conditions when the authigenic carbonates were precipitated. In particular, concentrations of redox-sensitive elements such as Mn and Fe were increased in bottom waters and sedimentary pore waters under oxygen-depleted conditions in the Landsort Deep, which resulted in Mn- and Fe-enriched carbonate formation. The diagenetic alteration on foraminiferal tests provides potential opportunity to investigate past sedimentary redox environment and primary productivity in the Baltic Sea.

How to cite: Ni, S., Quintana Krupinski, N., Groeneveld, J., Knudsen, K. L., Persson, P., Somogyi, A., Brinkmann, I., Seidenkrantz, M.-S., and Filipsson, H. L.: Early diagenesis in benthic foraminifera under anoxic conditions from the Landsort Deep, Baltic Sea (IODP Site M0063), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8653, https://doi.org/10.5194/egusphere-egu2020-8653, 2020.

A numerical reaction transport model was developed to simulate the effects of microbial activity and mineral reactions on the composition of the porewater in a 150-m-thick sedimentary interval drilled in the Peruvian deep-sea trench (Ocean Drilling Program, Site 1230). This site shows a zone of intense methanogenesis below 10 m sediment depth. The simulation shows that microbial activity accounts for most alkalinity production of up to 150 mmol/l, while the excess of CO₂ produced during methanogenesis causes a strong acidification of the porewater. Ammonium production from organic matter degradation significantly contributes to alkalinity production, whereby ion exchange was simulated to compensate for hidden ammonium production not otherwise accounted for. Although clay minerals are reacting far too slowly to equilibrate with the porewater over millions of years, additional alkalinity is provided by alteration of chlorite, illite, and feldspar to kaolinite. Overall, alkalinity production in methanogenic zones is sufficient to prevent dissolution of carbonates and to induce carbonate formation either continuously as disseminated cryptic dolomite or episodically as hard lithified beds along a supersaturation front. The simulation presented here provides fundamental insight into the diagenetic effects of the deep biosphere and may also be applicable for the long-term prediction of the stability and safety of deep CO₂ storage reservoirs.

How to cite: Herda, G., Petrishcheva, E., Gier, S., Liu, B., and Meister, P.: Microbial alkalinity production and clay mineral alteration in marine methanogenic sediments: implications for diagenetic carbonate formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9810, https://doi.org/10.5194/egusphere-egu2020-9810, 2020.

Stromatolites are laminated, presumably microbial structures, consisting largely of an authigenic precipitate, thus, providing potential geochemical archives of early Earth aqueous environments and their habitability. In this study, we report trace element and Sm/Nd isotope data from Palaeoarchean stromatolites and adjacent cherts of the Strelley Pool Formation (NW Australia), obtained by ICP-MS and TIMS, to test their reliability as archives for palaeo-environmental reconstruction and to understand authigenic mineral formation.

Stromatolitic carbonates plot together with the stratigraphically underlying Marble Bar cherts on a linear Sm-Nd regression line yielding an age of 3253 ±320 Ma.. In contrast, associated crystal-fan carbonates yield 2718 ±220 Ma, suggesting that their Sm-Nd isotope system was altered after deposition. Geochronological information via Sm-Nd dating of black and white cherts is limited, probably due to a reset of the isotope system during an unknown Paleoproterozoic or younger alteration event.

Carbonates, as well as white cherts, show shale-normalized rare earth element and yttrium patterns (REY_SN; except for redox-sensitive Ce and Eu) parallel to those of modern seawater, indicating a seawater-derived origin. Positive Eu_SN anomalies (2.1 - 2.4), combined with heterogeneous ɛNd_3.35Ga values (-3.2 to +5.8) within alternating stromatolite laminae, support that seawater chemistry was variably affected by both continental weathering and high-temperature hydrothermal fluids contributing elements of both young mafic or older felsic rocks. In contrast, black cherts show non-seawater like REY_SN patterns and significant amounts of elements leached from the surrounding rocks, masking the pristine geochemical composition of ancient seawater. In conclusion, Archaean stromatolites indeed preserve pristine authigenic phases at the mm-scale that contain signatures representative of the water chemistry prevailing in the depositional environment.

How to cite: Viehmann, S., Hohl, S. V., Tepe, N., Van Kranendonk, M., Reitner, J., Hofmann, T., Koeberl, C., and Meister, P.: Carbonate and chert genesis in the 3.35 Ga old Strelley Pool Formation (Australia): Insights from trace metals and Sm/Nd dating , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6909, https://doi.org/10.5194/egusphere-egu2020-6909, 2020.

The carbonate skeletons of marine organisms are unique archives for high-resolution climate reconstructions. Well-preserved specimens potentially allow for seasonal to even daily scale variability reconstructions of climate and environment  in deep time (pre-Quaternary), providing otherwise unavailable snapshots of climate variability during greenhouse periods (e.g. Steuber et al., 2005; Ivany et al., 2008; de Winter et al., 2017). However, uncertainties on past seawater compositions hamper use of the popular stable oxygen isotope ratio (δ¹⁸O) as proxy for paleotemperature reconstructions. The use of the independent carbonate clumped isotope (Δ₄₇) paleothermometer, which is insensitive to changes in seawater composition, on these promising fossil archives is complicated because of sample size limitations (Fernandez et al., 2017; Bernasconi et al., 2018).

In an attempt to circumvent these issues and use the δ¹⁸O and Δ₄₇ measurements jointly for accurate seasonal reconstructions of temperature and seawater isotope composition, we present a novel data reduction approach that combines Δ₄₇ measurements of small (~100 µg) serially sampled aliquots to estimate summer and winter temperatures in mollusk shell records. When applied on Δ₄₇ and δ¹⁸O measurements in the same specimens, combined with accurate shell chronologies, this approach reconstructs seasonal differences in temperature and seawater composition in a coastal site from the Campanian (Late Cretaceous) high-latitudes.

To test the robustness of these reconstructions, we apply different approaches of combining δ¹⁸O and Δ₄₇ data on a wide range of simulated data representing various scenarios of variability in growth rate, temperature and sea water composition typical for the natural shallow marine environments of carbonate-producers. This approach tests how choices such as sampling resolution and the method of data collection and reduction influence the accuracy and reproducibility of (paleo)seasonality reconstructions in these scenarios.

Finally, we present preliminary data of δ¹⁸O and Δ₄₇ analyses on bivalve specimens grown under controlled temperature conditions that allow us to calibrate the techniques above for temperature reconstructions. Together, these investigations pave the way for accurate, high-resolution climate reconstructions in deep time. These reconstructions provide valuable information on the dynamics of greenhouse climates, against which climate models can be compared to improve predictions of future climate.

References

Bernasconi, S. M., et al. Geochemistry, Geophysics, Geosystems, 19(9), 2895–2914, 2018.

Fernandez, A. et al. Geochemistry, Geophysics, Geosystems, 18(12), 4375–4386, 2017.

Ivany et al. Geological Society of America Bulletin, 120(5–6), 659–678, 2008.

Steuber, T. et al. Nature, 437(7063), 1341–1344, 2005.

de Winter, N. J. et al. Palaeogeography, Palaeoclimatology, Palaeoecology, 485, 740–760, 2017.

How to cite: de Winter, N., Witbaard, R., Ullmann, C., Soerensen, A., Thibault, N., Müller, I., Kocken, I., Claeys, P., and Ziegler, M.: Absolute temperature seasonality from skeletal carbonates—Techniques and limitations of oxygen- and clumped isotope analyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2842, https://doi.org/10.5194/egusphere-egu2020-2842, 2020.

The shells of oysters (Family Ostreidae) are predominantly composed of two different calcite microstructures: A dense foliated structure consisting of sheet-like folia (“foliated” microstructure) and a more porous microstructure consisting of less well organized leaf-shaped crystals (“chalky” microstructure). These unique characteristics of oyster shells have been subject to a number of studies, with some authors hypothesizing that the chalky structures are mineralized by bacteria living in the shell (Vermeij, 2014). The formation of these microstructures is of great interest, because the phenomenon is unique in the mollusk phylum and because the shells of oysters are popular archives for paleoclimate and paleoenvironment reconstructions (e.g. Bougeois et al., 2018; de Winter et al., 2018). Previous authors have challenged the bacterially mediated mineralization hypothesis through microstructural observations of different parts of the oyster shell (Checa et al., 2018).

Here, we expand on this structural evidence by adding detailed observations of differences in chemical composition between the foliated and chalky microstructures. We combine information on trace element concentrations with stable carbon, oxygen, nitrogen and sulfur isotope ratios as well as carbonate clumped isotope analyses of samples from foliated and chalky structures in multiple modern specimens of Magallana gigas, the Pacific oyster. These analyses shed light on the chemical variability within the oyster shell and how it relates to the occurrence of various calcite microstructures. Given the unique isotopic signature of bacterially mediated calcite, our isotopic analysis results allow us to definitively conclude whether the chalky shell structure in modern oysters was precipitated via symbiotic microbes. Furthermore, the degree of intra-shell chemical variability has implications for paleoclimate and paleoenvirionmental reconstructions from fossil oyster shells, for which the applied trace element and isotope systems function as important proxies. The results of this study therefore yield important recommendations for sampling fossil oyster shells for reconstructions, and provide a baseline for the investigation of chemical variability between shell microstructures throughout the Ostreidae family and the mollusk phylum.

References

Bougeois, L., Dupont-Nivet, G., De Rafélis, M., Tindall, J. C., Proust, J.-N., Reichart, G.-J., de Nooijer, L. J., Guo, Z. and Ormukov, C.: Asian monsoons and aridification response to Paleogene sea retreat and Neogene westerly shielding indicated by seasonality in Paratethys oysters, Earth and Planetary Science Letters, 485, 99–110, 2018.

Checa, A. G., Harper, E. M. and González-Segura, A.: Structure and crystallography of foliated and chalk shell microstructures of the oyster Magallana: the same materials grown under different conditions, Scientific reports, 8(1), 7507, 2018.

Vermeij, G. J.: The oyster enigma variations: a hypothesis of microbial calcification, Paleobiology, 40(1), 1–13, 2014.

de Winter, N., Vellekoop, J., Vorsselmans, R., Golreihan, A., Soete, J., Petersen, S., Meyer, K., Casadio, S., Speijer, R. and Claeys, P.: An assessment of latest Cretaceous Pycnodonte vesicularis (Lamarck, 1806) shells as records for palaeoseasonality: a multi-proxy investigation, Climate of the Past, 14(6), 725–749, 2018.

How to cite: Dämmer, L. K., de Winter, N. J., Falkenroth, M., Reichart, G.-J., Moretti, S., Martinez-García, A., Höche, N., Rodiouchkina, K., Goderis, S., Vanhaecke, F., and Ziegler, M.: A chemical investigation of microstructural changes in oyster (Magallana gigas) shells, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4506, https://doi.org/10.5194/egusphere-egu2020-4506, 2020.

There are numerous similarities between the otolith (an acellular calcium carbonate aggregate in the inner ears of fishes) and the shells of freshwater bivalves. Since both grow during a lifetime of the individuals, and show small increments or growth zones (in daily or subdaily periods), they are excellent time-keepers. By this capability they provide information about both the life history of the individuals and the geochemical evolution of their environments (Schulz-Mirbach et al., 2018; Cerrato, 2000). Changes of major and trace elements between the different growth zones have been studied thoroughly, but structural features, particularly those of otoliths, are not well known. We used scanning and scanning transmission electron microscopy (SEM and STEM) to study oriented ion-milled sections of an otolith and samples of Dreissena shells from Lake Balaton, a large, shallow lake in Hungary. SEM observations confirm that the growth zones within the otolith are built up of small increments, and they have a radially asymmetric appearance, whereas STEM images show that the small increments are terminated by tiny holes. Selected-area electron diffraction (SAED) patterns and HRTEM images show that the aragonite material of both samples is highly defective, with dense arrays of planar defects occurring in distinct areas, and grains joining along low-angle boundaries (around 1°). In addition, areas with multiple (double and triple) periodicities along the [110]* directions occur in both samples. Based on these preliminary observations, nanostructural features could provide important details about the growth of biogenic aragonite and the structural properties of distinct growth zones.

Cerrato R. M. (2000): What fish biologist should know about bivalve shells, Fisheries Research, 46, 39-49.

Schulz-Mirbach T., Ladich F., Plath M., Heß M. (2018): Enimgatic ear stones: what we know about the functional role and evolution of the fish otoliths, Biological Reviews, 94 (2), 457-482.

Acknowledgments: The research was supported by the ÚNKP-19-3 new national excellence program of the ministry for innovation and technology. 

How to cite: Molnár, Z., Pekker, P., Jakab, M., Dódony, I., Vitál, Z., and Pósfai, M.: Nanostructure of biogenic aragonite: a study of otoliths and bivalve shells from a freshwater environment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21996, https://doi.org/10.5194/egusphere-egu2020-21996, 2020.

Brachiopods present a key taxon for Phanerozoic palaeo-climatic and palaeo-environmental reconstructions, owing to their good preservation and abundance in the geological record. Yet to date, only little is known on the mechanisms that control the incorporation of some key elements into their calcitic shells, as well as the mechanisms behind the biomineral formation itself, especially in thecideid brachiopods. To evaluate the distribution and controls on Mg, Ca, and Sr we examined the composition of natural Pajaudina atlantica Logan, 1988 (Thecideidae, Brachiopoda) originating from Canary Islands, Spain as well as specimens cultured experimentally under various pH-pCO₂ and temperature conditions [1]. At a high-spatial resolution, electron microprobe analyses (EMP) revealed substantial intrashell and intraspecific Mg and Ca heterogeneities that seemed to be principally linked to growth features and different microstructures rather than changes in temperature. Strontium, on the other hand, appeared uniform across the shell and related to the culture medium or seawater Sr content. After almost two years of culturing, however, the new shell production was only minimal and cryptic, and difficult to evaluate by visual inspections. By combining culture-specific geochemical fingerprints with radiocarbon dating of natural samples, we estimated the growth rates to be on the order of several tens to few hundreds of µm per year, which may potentially suggest a large life span and slow growth of this species, and if true, would certainly make them a highly interesting archive for inferring past ocean variabilities.

[1] Jurikova H., et al. (2019) Geochim. Cosmochim. Acta 248, 370–386.

How to cite: Liebetrau, V., Jurikova, H., Gutjahr, M., Henkel, D., Hiebenthal, C., Krause, S., and Eisenhauer, A.: Magnesium, calcium, strontium and radiocarbon in the shell of the brachiopod Pajaudina atlantica: implications for growth, biomineralisation and palaeo-proxy application, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19006, https://doi.org/10.5194/egusphere-egu2020-19006, 2020.

Bamboo corals are calcitic octocorals dwelling in a broad range of water depths and in all ocean basins. Their skeletons could give insight into the temporal variability of environmental parameters at their growth locations, in areas where long-time observations are often lacking. A thorough understanding of calcification mechanisms is essential to interpret the chemical composition of their high-magnesium calcite skeleton regarding environmental fluctuations of the deeper ocean. To address this issue, we employed electron microprobe analysis, confocal Raman spectroscopy, laser ablation-ICPMS and solution based multi collector-ICPMS that together provide insights into the fine-scale spatial heterogeneity of the coral chemical composition. We investigate the spatial distribution of Na, S, and Ca, as well as organic matter in skeletal sections of specimens of Keratoisis grayi (family Isididae) from the Atlantic Ocean. Two bamboo coral samples from the Atlantic and Pacific Ocean were further used to create laser ablation-based maps of δ¹¹B and boron to carbon ratios (B/C) over the sample radii. These maps are compared with results obtained via solution based δ¹¹B analyses on drilled samples.

An inverse correlation between Na and S is observed while S seems to be positively correlated with organic matter. We will discuss the ability of a qualitative physicochemical model to explain the observed Na and S distribution and the potential role of organic matter and amorphous calcium carbonate. Our results indicate that skeletal Na/Ca in bamboo corals is largely driven by physiological processes rather than environmental salinity variability. The spatial distribution of δ¹¹B shows a positive correlation with B/C. The observed range of bulk δ¹¹B - partly falling below the theoretical borate fractionation curve in seawater - is larger than the conventional measured δ¹¹B of the calcite fraction alone. The latter cannot be explained with a spatial smoothing of the distribution during sample drilling but is rather associated with a loss of an isotopically highly variable B fraction during sample bleaching. Potential reasons for the observed differences in B isotopic range and their implications will be presented. We conclude that skeletal δ¹¹B as a proxy for pH_SW is dependent on the applied technique and investigated material fraction.

How to cite: Flöter, S., Fietzke, J., Gutjahr, M., Farmer, J., Hönisch, B., Nehrke, G., and Eisenhauer, A.: Isotopic and elemental mapping of bamboo corals – reference to calcification mechanism and proxy applications , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10590, https://doi.org/10.5194/egusphere-egu2020-10590, 2020.

Despite their omnipresence in pelagic carbonate sediments, the coccoliths, the calcite biominerals produced by the coccolithophores, have historically been under-exploited in palaeoenvironmental studies. This is due, in part, to their small size (2-20 microns), which makes them difficult to isolate from other particles, and to the large differences in isotopic composition existing between coccolith calcite and equilibrium conditions. This so-called “vital effect” complicates the use of coccolith geochemistry to derive paleoclimatic signals with confidence. Recent studies from cultured and fossil coccoliths have shown that the oxygen and carbon isotopic compositions of the coccoliths are particularly sensitive to the availability of CO₂ in the environment, upon which the coccolithophores rely for their photosynthetic activity. Therefore, our approach here is to test whether the coccolith geochemistry can be used as a novel proxy for surface ocean and atmospheric CO₂ concentrations.

In this study, different size fractions of coccoliths were extracted from carbonate sediments of site MD95-2037 in the Northern Atlantic Ocean and run for isotopic analysis. Using calibrations between coccolith vital effects and seawater [CO₂] from culture studies, we present a seawater [CO₂] curve for site MD95-2037 across Termination II (130 kyrs). The curve was in turn translated into atmospheric pCO₂ estimates taking into account changes in ancillary parameters (such as temperature). Coccolith-derived CO₂ concentrations yield comparable values, both for the absolute numbers and trends, to the record from Vostok ice cores. This coherency is confirmed by a 80 ppm-shift in pCO₂ concentrations in the North Atlantic between glacial and interglacial times reconstructed from the coccolith record.

Altogether, these datasets confirms that coccolith geochemistry can indeed be used to reconstruct past changes in [CO₂]_sw. Perspectives for this study include providing the scientific community with a new record of pCO₂ for periods extending beyond the Vostok record, in particular the Mid-Pleistocene Transition, where a decrease in global pCO₂ has been put forward to explain the shift from 41 kyr- to 100 kyr-cycles in glacial-interglacial cycles.

How to cite: Godbillot, C., Hermoso, M., and Minoletti, F.: Probing the use of coccolith geochemistry as a proxy for past carbon dioxide concentrations - Insights from Termination II in the Northern Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7471, https://doi.org/10.5194/egusphere-egu2020-7471, 2020.

Coccolithophores play an important dual role in ocean biogeochemistry: they use dissolved inorganic carbon (DIC) in the surface for both photosynthesis and coccolith calcification. Stable isotopes in coccoliths are the result of various effects, including different vital effects, allowing hypotheses about the varying active carbon acquisition strategies in response to changing environmental conditions. Understanding the physiological mechanisms that cause these changes remains challenging.

The MIS 12 to MIS 9 interval is a crucial climatic period encompassing changing glacial-interglacial cyclicity and pronounced variations in atmospheric CO₂ concentration. Different paleorecords indicate that coccoliths were an important component of the carbonate fraction during this interval, with the outstanding worldwide dominance of the highly calcified coccolithophore species Gephyrocapsa caribbeanica.

The carbon isotopic fractionation during photosynthesis (εp) in alkenones, biomarkers produced by coccolithophores, is a proxy to reconstruct past aqueous CO₂ concentration. Here we present a new εp reconstruction spanning this glacial/interglacial interval (460 to 330 kyr) at ODP Site 925 in the western tropical Atlantic. We aim to evaluate the interplay of CO₂ and productivity effects on coccolith calcification and stable isotopes (δ¹⁸O and δ¹³C) in coccolith calcite integrating these data with the size and thickness of coccolith platelets and the geochemical Sr/Ca record.

The comparison of mean coccolith size with coeval samples from the deeper ODP Site 929 allows the evaluation of the degree of nannofossil dissolution across the interval.

How to cite: González-Lanchas, A., Stoll, H. M., Flores, J.-A., Sierro, F. J., Hernandez-Almeida, I., and Guitian, J.: The interplay of glacial/interglacial climate-CO2 and productivity effects on coccolith calcification and vital effects across the MIS 12 to MIS 9 in the western tropical Atlantic , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19299, https://doi.org/10.5194/egusphere-egu2020-19299, 2020.

We cultured two species of Amphistegina under four pCO₂ concentrations yielding variable pH (8.1 -7.6) and DIC (2340-2570 μM) at constant temperature (25 ºC) and alkalinity (~ 2500 μM). To mark the newly grown shells under the experimental conditions we spiked the culture seawater with ¹³⁵Ba. The variability of trace elements within the foraminiferal shells was measured on three individuals of each species for each treatment using LA-ICPMS in the knob area. Sharp transition zones were observed between the natural and the ~tenfold increased ¹³⁵Ba in the shells. The shape of the transition zone is best described by a logistic equation for population growth. We propose that this reflects the dynamics of seawater vacuoles population that serve the biomineralization process and provide Ca and DIC for calcification of Amphistegina as described in previous publications (e.g. Bentov et al., 2009). In individuals that showed significant growth (identified by ¹³⁵Ba-enriched shell), B, Na and Sr showed a significant increase with DIC, while K and Mg were slightly lower or unchanged. LA-ICPMS profiles in the central knob (~70 µm depth) also revealed previously described cyclical changes in concentration of Mg, each apparently representing a growth of a new chamber. Additional elements such as K, Na and U showed similar cycles with the same frequency and phase as the Mg cycles. Sr showed variability with similar frequency but not in-phase with those of the Mg. These multi-element cycles were found both in the newly grown calcite (elevated-¹³⁵Ba and pCO₂) and in the natural skeleton regardless of the pCO₂ treatments. These high Mg and multi-element cycles seem to be an essential part of the calcification process. They may originate from the interaction with the organic matrix resulting in elevated Mg and other elements in the primary calcite while secondary calcite of the lamination process shows lower concentrations. It is also possible that primary calcite is enriched in trace elements if an Amorphous CaCO₃ (ACC) or vaterite precursors are involved. In addition, Rayleigh fractionation from a semi-closed reservoir, the presence of high Mg in the lattice or any combination of the previous causes may explain the trace elements enrichment. While changes in the pCO₂ did change the average concentrations of B, Na, and Sr, they did not affect the banding of trace elements in these foraminifera, suggesting that these cycles are inherent to the biomineralization process.

Bentov, S., Brownlee, C., and Erez, J. (2009). The role of seawater endocytosis in the biomineralization process in calcareous foraminifera. Proc. Natl. Acad. Sci. U.S.A. 106, 21500–21504. doi: 10.1073/pnas.0906636106

How to cite: Levi, A., Müller, W., and Erez, J.: The effect of high pCO2 on trace elements and intrashell variability: A culture experiment with live benthic foraminifera., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13080, https://doi.org/10.5194/egusphere-egu2020-13080, 2020.

Na is incorporated into marine carbonate minerals and was recently proposed as a proxy for paleo-salinity. However we demonstrated that Na/Ca ratio in foraminiferal shells (Na/Ca_shell) is actually a novel proxy for past ocean Ca concentrations (Ca_sw) in benthic foraminifera (Hauzer et al., 2018). In the present study, we determined the extent to which foraminiferal Na/Ca (and other elements) change with salinity for the high-Mg large benthic foraminifer Operculina ammonoides. This laboratory culture experiment was conducted under four different salinities 32.9, 36.1, 40.65 and 43.0 PSU, at a constant temperature of 25 °C and pH of ~8.17. O. ammonoides specimens were labeled with the fluorescent dye Calcein (40 µM) for five days prior to the experiment. Experimental seawater was prepared from filtered Gulf of Eilat seawater (40.65 PSU) and the salinity was modified by the addition of deionized water or by the evaporation to the desired value at room temperature. All experimental seawater were spiked with ¹³⁵Ba in order to unambiguously determine newly grown CaCO₃ during spatially-resolved analysis of the shell. Six specimens of each treatment were selected according to the presence of non-fluorescent chambers past the Calcein mark. The CaCO₃ shells were analyzed using the LA-ICPMS. Water chemistry was analyzed using ICP-OES and ICP-MS. Experimental foraminifera added 90-160% of their original weight, based on alkalinity-depletion measurements during the experiment. The elemental ratios of Na, Mg and Li to Ca in O. ammonoides shells increased linearly with increasing seawater salinity. In contrast, Sr/Ca_shell showed no resolvable change with salinity. Since Na/Ca_shell does correlate with salinity, it appears that it could be used as a paleosalinity proxy. However, when variations of Na/Ca_shell due to salinity are compared to variations due to Ca_sw, it is clear that salinity has a minor effect compared to the Ca concentrations. Thus, when reconstructing paleosalinity, Na/Ca_shell will produce accurate results only for samples that are within the residence time of Ca_sw (~1My). Furthermore, regional and global changes in ocean salinity over geological time can only slightly affect the use of Na/Ca_shell as a proxy for past changes in Ca_sw.

Hauzer, H., Evans, D., Müller, W., Rosenthal, Y., & Erez, J. (2018). Calibration of Na partitioning in the calcitic foraminifer Operculina ammonoides under variable Ca concentration: Toward reconstructing past seawater composition. Earth and Planetary Science Letters, 497, 80-91.

How to cite: Hauzer, H., Evans, D., Müller, W., Rosenthal, Y., and Erez, J.: The effect of salinity on Na/Ca in cultured shells of the foraminifer Operculina ammonoides, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17249, https://doi.org/10.5194/egusphere-egu2020-17249, 2020.

The calcite shells of planktonic foraminfera are a key archive for palaeoceanic reconstruction and represent one of the largest sinks of carbon from the surface ocean. Therefore, understanding the biomineralisation process of these organisms, and how responsive it is to ocean acidification, is an important part of accurately predicting the carbon cycle response to past and future climate change events. To date, the majority of the direct observational evidence on which foraminifera biomineralisation models are based comes from shallow-dwelling benthic species. Whilst this has provided a large amount of important information, it is not known how applicable these models are to the low-Mg planktonic foraminifera. In particular, key questions regarding the relative importance of seawater vacuolisation (SWV) versus calcium transmembrane transport (TMT) remain unresolved. We present the results of fluorescent labelling experiments on intact, decalcified planktonic foraminifera (Globigerinoides ruber and Globigerinella siphonifera) using the cell-impermeable dyes calcein, FITC-dextran, and SNARF-dextran, enabling direct observation of seawater vacuoles within the cell via confocal microscopy. Our results indicate that seawater endocytosis plays a dominant role in the calcification process. Seawater vacuoles can make up a large proportion of the intracellular volume, with a residence time on the order of hours. Moreover, we show that the skeleton is labelled with fluorescent dyes such that seawater derived from these vacuoles must be present at the calcification site. Along with inferences based on geochemical data [Evans et al., 2018], our results strongly argue that biomineralisation models centred on seawater endocytosis are applicable to the planktonic foraminifera.

Evans, D., Erez, J., Müller, W. [2018] Assessing foraminifera biomineralisation models through trace element data of cultures under variable seawater chemistry. GCA 236:198.

How to cite: Evans, D., Erez, J., and Müller, W.: Understanding the role of seawater vacuolisation in the biomineralisation of planktonic foraminifera using confocal microscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18090, https://doi.org/10.5194/egusphere-egu2020-18090, 2020.

The crystallization pathways of amorphous into crystalline orthocalciumphosphate phases is a widely discussed topic, with processes not yet entirely understood. Current research focuses on medical applications as well as natural sedimentary systems, for example bone-tissue-engineering, bio-mineralization and phosphogenesis, with inorganic precipitation experiments under controlled ambient conditions being the first step to improve our understanding of the fundamental formation processes. By mixing of stock solutions with CaCl₂/MgCl₂ and NaHPO₄ we created a supersaturated solution in respect to CaPO₄-phases and varied the pH by adding different amounts of NaOH. Continuous sampling was performed over the period of 24 hours, with sampling intervals after 1 min, 10 min, 60 min and 24 h. In order to record temporal changes in mineralogical and chemical composition, samples (solids and fluids) were investigated by XRD, FTIR, SEM and ICP-OES, respectively. Our experiments yield considerable differences concerning the time of amorphous calcium phosphate (ACP) transformation into hydroxyapatite (HAP), heavily depending on the pH, Ca/P ratio and Mg content of the stock solution. Main results show that a higher pH stabilizes the ACP over a period of the first 60 min, whereas at lower pH the transformation of ACP into the crystalline phase already starts at 10 min after mixing. Increasing the Ca/P ratio of the stock solution results in ACP being less stable and the transformation into HAP occurs earlier. In contrast, the presence of Mg seems to delay the formation of HAP via ACP. After 24 hours the experiments showed nano-crystalline HAP and most likely some other phases as octacalcium phosphate.

How to cite: Hippler, D., Schnedlitz, T., and Purgstaller, B.: Investigating the reaction pathway of crystalline orthocalciumphosphate formation via amorphous precursors in respect to different pH, Ca/P ratios and Mg presence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20510, https://doi.org/10.5194/egusphere-egu2020-20510, 2020.

Sand volume and porosity measurements on sandstones are routine work in geoscientific applications, providing useful input to flow simulation in porous media-based analyses (e.g., in CO₂ storage and/or hydrocarbon migration studies). The classic way to gain knowledge about these parameters is point counting on thin sections. This time-consuming, repetitive, and subjective work is usually done by an experienced petrographer. Attempts to automate and digitize this process are therefore promising. An example using image analysis has been discussed in Roduit, 2007. However, one step further is combining image analysis with machine learning.

In this work, we evaluate the use of a neural network learning algorithm to classify selected sandstone properties from thin section images. Our database consists of ca. 3500 thin section images from different sandstone types with known properties. The images are grouped into 8 different sand volume and 8 different porosity classes. We split the dataset into a training (85 %) and validation dataset (15 %). In the processing stage, we normalize and scale all the images to a reference number of 128 pixels. For both classifications, we trained a convolutional neural network consisting of 5 convolutional layers and 4 max pool layers. The batches are normalized after each pooling layer and a dropout layer used to reduce overfitting before flattening. A final soft max layer is added so that the recovered output can be interpreted as probability distributions. We perform the training phase with a varying number of epochs ranging between 20 and 200. A training and validation accuracy > ca. 90 % is obtained after 25 epochs. For both cases, we observe that initially high model loss for the validation data reaches low values after 50 epochs.

To further test the approach, we analyse in a second stage a holdout dataset of sandstones from the Norwegian Continental Shelf. Preliminary results show that the derived sand volumes classification reproduce the point counting results well (80 % accuracy of predicting classes or neighbouring classes). More problematic is the reproducibility of porosities. Here, models using different epochs show variable results and the ≥100 epochs models systematically underestimates the measured rock porosities. We observe that only porosity classes well represented in the initial population of training images are reproduced with high accuracy. We finally discuss strategies to overcome such limitations.

Roduit, N., 2007. JMicroVision: un logiciel d'analyse d'images pétrographiques polyvalent. PhD Thesis University of Geneva,116 pp. 

How to cite: Emmel, B., Roli, O.-A., and Romdhane, A.: Machine learning to identify sandstone properties from thin sections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4697, https://doi.org/10.5194/egusphere-egu2020-4697, 2020.

Information about the distribution microplastics is crucial in marine environmental research. At present, plastic pollution is an environmental threat to the oceans and more than 90 % of microplastic particles are assumed to be deposited in the sediments on the ocean floor. An efficient way of identifying microplastic particles in marine sediments would result in improved understanding of microplastic distribution, inception, accumulation areas, and impact on marine ecosystems. Today, manual classification of microplastic particles using a microscope is time consuming. The goal of this study is to identify microplastic particles in marine sediment samples with the help of image recognition and machine learning. The possibility of using artificial microplastic particles will also be tested as a means of constructing comprehensive training sets. Existing algorithms already have been successful in classification of microfossils, which could be further developed for recognition of microplastic particles. Furthermore, hyperspectral analysis will be tested to determine the origin of the microplastic particles. Our overall goal is to train classifiers that in the future successfully can recognize different plastic objects in marine sediment samples and thereby replace the time-consuming manual classification task. Comparison between human based and machine based identifications for a large number of data sets will be made to test these classifiers.

How to cite: Junttila, J., Aagaard Sørensen, S., Haugland Johansen, T., and Wing Gabrielsen, G.: Image recognition of microplastic particles in marine sediments – planned activities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7858, https://doi.org/10.5194/egusphere-egu2020-7858, 2020.

Foraminifera are microscopic single-celled organisms, ubiquitous to the marine realm, that construct shells during their life cycle. The shells, in general, fossilize well in the sediment and they are diagnosable due to inter-species morphology and ornamentation variability. Classifying and counting foraminiferal shells is an important tool in assessing and reconstructing past and present environmental, oceanographic and climatological conditions. However, the present day manual identification procedure, performed with a microscope and a needle/brush, is a very time consuming. Circumventing this manual procedure, using machine leaning, promises to dramatically lower the time consumption related to generating foraminiferal data records.

The first step towards that end is developing a deep learning model that can detect and classify microscopic foraminifera from 2D digital microscope pictures. The work is based on a VGG16 model implementation that has been pre trained on the ImageNet dataset and employing transfer learning techniques to adapt the model to the foraminifera task. The 2D photographic training data input was constructed by combining objects representative of and extracted from Arctic marine sediments (100µm-1mm size fraction) from the Barents Sea region. Four object groups, including 1) calcareous and 2) agglutinated benthic foraminifera, 3) planktic foraminifera and 4) sediments were used in the training data construction. With the initial set-up the algorithms were able to identify adherence to one of the four groups correctly ~90% of the time and with further fine-tuning and refinement reaching 98% correct identifications.

The second step is to use machine leaning for classification of individual benthic calcareous foraminiferal species within the sediment. The work will focus on the 20 most common species that comprise ca. ≥ 80% of the total benthic calcareous foraminiferal fauna in the Arctic. The training of the algorithms will be done using targeted species-specific 2D photographic and 3D CT scanning data in addition to potentially using hyperspectral imaging.

How to cite: Aagaard-Sørensen, S., Haugland Johansen, T., and Junttila, J.: First-order machine learning based detection and classification of foraminifera in marine sediments from Arctic environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7606, https://doi.org/10.5194/egusphere-egu2020-7606, 2020.

Recent progresses in image processing, and image recognition have paved the way for automated procedures to classify natural objects such as foraminifera. Foraminifera are among the most useful tracers in biostratigraphy and paleoceanography. Yet, the protocol used to extract and recognize the foraminifera has not changed since the mid-18^thcentury: manual picking using a brush with a stereomicroscope.

Here we present the results we achieve by developing the MiSo - Microfossil Sorter - automaton, to automatically pick microfossils from the sediment coarse fraction. This automated system, built with ATG Technologies, is fully operational and works 24/7 at CEREGE. In this study, we will detail the basic workflow of the automaton, processing ~8000 particles/day, and its ability to cope with the large morphological and structural variability of particles encountered in real, marginal to deep-sea sediments. We use convolutional neural networks adapted and trained on deep sea sediment samples to classify the coarse sediment particles, including planktonic and benthic foraminifera.

As a test case, we will compare paleoceanographic records generated by a micropaleontologist with the ones generated by our automaton: relative abundance, fragmentation rate, biometrical changes. We have studied two deep-sea cores from the equatorial Pacific to document past hydrographic changes in the late Quaternary, achieving millennial scale resolution through the last deglaciation. Using the automaton, we processed more than 500,000 foraminifera. The accuracy of recognition typically ranges around 85 to 95% depending of the morphoclasses and of the CNN used for the training. Morphoclass size probability density function and assemblages derived from the CNN will be compared to multi-proxy (micropaleontological and geochemical) records. We will discuss the ongoing applications of our workflow, from foraminifera to pteropods in deep sea sediments, and the recent updates of our system.

How to cite: de Garidel-Thoron, T., Marchant, R., Tetard, M., Adebayo, M., and Gally, Y.: Automated recognition and picking of foraminifera using the MiSo (microfossil sorter) prototype, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18067, https://doi.org/10.5194/egusphere-egu2020-18067, 2020.

One of the best methods for studying past climate variability is the analyses of microfossils in sediment cores, especially foraminifera. However, this is highly laborious and time-consuming work. Consequently, several independent endeavors are currently underway with the aim of to automate this procedure, each testing different techniques. Here, we present preliminary results of one of these endeavors that focus on benthic foraminifera from arctic and temperate regions. The study is based on ongoing student projects carried out in collaboration between engineers and geologists. We combine robotics, imaging and machine learning.

The project is divided into three stages, with stage 1 and 2 currently ongoing: 1) Robotic separation of foraminiferal specimens from sediment particles, 2) Species classification algorithm based on Convolutional Neural Networks (CNN) including creation of training material. 3) System verification comparing analyses carried out by the automated system and a foraminiferal specialist on the same dataset. Phase 3 has not yet commenced, but initial results of 1 and 2 are available. In time, we hope to be able to build up a database of about 100 different foraminiferal species, which will cover the main assemblages of the coastal regions of the Arctic and Atlantic cold temperate regions.

For separating and picking of specimens (1) we have evaluated two different methods using a custom made xyz-platform or a robotic arm. Based on this, it seems that moving the specimens with a robotic arm will work well, but the price of such a robotic arm makes this solution less practical. In contrast, the combination of separating the specimens through shaking the sample in a tray and picking specimens for photographing and analyses using a suction system, with a custom made xyz-platform, is the best solution when considering quality, speed and price. Subsequently, the picked foraminifera/grains are delivered automatically to a digital microscopy system and photographed. So far focus on this part of the process has been developing a precise system for moving and picking, and in the future, we will work towards being able to handle particles of highly variable size in the same sample as well as increasing the speed of the picking and photographing process. 

For foraminiferal identification (2), parts of the labeling process have been automated using the Django (Python) framework and Amazon Web Services. Also, a number of imaging experiments have been investigated and several Convolutional Neural Network (CNN) algorithms are being developed and tested. In this first test, we include three different benthic foraminiferal species, with very distinct morphologies, as well as various types of clastic grains in approximately the same size fraction as the foraminiferal individuals. In this initial test case only relatively few specimens were included in the database (Ammonia batava - 168 specimens, Elphidium williamsoni - 168 specimens and Quinqueloculina seminulum specimens - 168 specimens as well as 449 clastic grains). Using a customized CNN algorithm, the separation of foraminifera from mineral grains and foraminiferal species identification could be carried out respectively with a precision, recall and F1-score of 94% and 91%.

How to cite: Seidenkrantz, M.-S., Melvad, C., Bjerge, K., Ahrendt, P., Broeders, E. J., Christensen, A. O. B., Førrisdahl, M., Poulsen, T., and Skov, E.: Foraminiferal sorting and identification: preliminary results of a test phase, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5953, https://doi.org/10.5194/egusphere-egu2020-5953, 2020.